SHEET METAL STAMPING IN AUTOMOTIVE INDUSTRY
SHEET METAL STAMPING IN AUTOMOTIVE INDUSTRY
STEEL PANELS IN CAR BODY STRUCTURE
Ever increasing competition in automotive industry demands productivity improvements and unit cost reduction. The manufacturing engineers and production managers of car body panels are changing their strategy of operation. The days of ‘a simple washer to a very complicated fender, all in plant stamping facility’, are gone. In-house manufacturing facilities preferably produce only limited number of major car panels, Fig. 5.1.
Fig. 5.1 Major Panels of Car Body
An automotive plant today produces some 40~50 critical panels per model of car in-house, that require some 100~150 dies.. Criteria for taking decision about the panels to be manufactured in-house vary from company to company. Very lately, the stamping plant of the automobile manufacturers includes the types of panels as given below in-house:
1. External (skin) panels, such as fenders, bonnet, decklid, roof, side panels, doors, etc. Some of these are two panels in a set as left hand and right hand
2. Internal mating panels, such as bonnet inner, decklid inner or door inner deciding subassembly quality
3. Dimensionally critical inner panels that are complicated either because of their complex shape or severe draw condition, such as, floor pans, dash panel, etc.
Automanufacturers prefer to procure the medium and small size panels from vendors depending on the availability (nearer facilities are preferred) and their capability to meet demanded specifications. Some are even farming out the major subassemblies such as doors to specialised vendors. Trends are for farming out as much as possible. The
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automobile plants are trying to concentrate on assembly operations, leaving specific technology related manufacturing, such as machining and pressing as separate facilities.
MATERIALS FOR BODY PANELS
Materials for car body panels require certain specific characteristics to meet the industry’s challenges: rationalisation of specifications for leaner inventory, improved formability for reduced rejection rate and better quality. Higher Strength Low Alloy (HSLA) steels of thinner gauges, are getting preference for weight reduction and the resulting better fuel economy. Other quality characteristics under demand are higher yield stress (strength), toughness, fatigue strength, improved dent resistance as well as corrosion resistance in materials used for body panels for improved durability and reliability.
To obtain consistent quality of autobody skin panels without failures during stamping, the formability/ductility specifications of strip steels are the basic requirements. The numerical values of the strain hardening exponent (n-value), the plastic anisotropy (r-value), and the forming limit diagrams for the sheet steels provide the index of formability of the panels. Strain hardening to some extent improves the dent resistance. Strain gradients in pressings are not to be unduly severe causing splitting and other related problems. To maintain the shape after the forming operation, minimal ‘spring back’ and high ‘shape fixability’ are also essential. As the panels are welded to shape the body structure with various arc/resistance welding operations, the weldabilty of the materials in use is very important. Finally, the specific roughness levels (textures) of the steel used for skin panels must be consistent and reproducible. It will be essential for the good adhesion of the various combinations of primers and paints used on autobody pressings to obtain high quality paint finishes (clarity of image and gloss).
Most of the steels used in automotive application are aluminium-killed steels of about 0.7 to 0.9 mm thickness. For inner automotive parts, drawing quality steels, such as SPCD (JIS G 3141), A619 (ASTM), CR3 (BS1449), and Sr13 (DIN 1623), while for outer panels requiring deep drawing such as fenders, hoods, oil pans, etc. Non-aging extra deep drawing steels such as SPCEN (JIS G 3141), A620 (ASTM), CR1 (Bs 1449), and St 14 (DIN 1623), are used. Aluminium-killed steels show little or no stretcher strains for a period of time sufficient to eliminate the need for roller-leveling. Thinner High Strength Low Alloy (HSLA) steels are being increasingly used for certain autobody components including skin panels. It must combine its high strength with a good level of formability, as a strength increase is always accompanied by a fall in formability. The improved bake hardening steels used specially for the external panels possesses sufficiently high formability and provides an increase in strength after the paint baking. A consequence of strength increase obtained during paint baking, is the improved dent resistance of the surface. Difficult autobody pressings of complex geometry have necessitated the use of steel grades with lower strengths too. Vacuum degassed microalloyed steels containing Ti and/or Nb additions are classed as Interstitial-free steels (IF-steels). IF-steels are being used with advantages of extremely high value of maximum drawing ratio, and the absence of the straining effect for difficult-to-form panels. Fig. 5.2 shows panels of High Strength Low Alloy steel, and Table 1 provides a list of special steels for different automobile panels.
Table 5.1 Special Steels for Different Automotive Panels
Steels for Auto Panels
Yield Strength, N/m2
Application conditions
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A. High Strength Steels
REPHOSPHORISED STEELS
􀃎 with additions of P upto
0.08 %
220~260
Autobody structural parts- door, roof, trunklid, hood,
pillar outer, rear floor, etc.
GRAIN REFINED STEELS
􀃎 appropriate alloy
additions which forms
typically NbCN, TiC
300~400
Formability relatively modest, so used for components with relatively less demanding forming
DUAL PHASE STEELS
􀃎 appropriate alloy additions
(Mn, Mo, Cr, V) and
processing
400~500
High strength, with good formability. Suitable for door, roof, trunklid, hoods, etc.
BAKE HARDENING STEEL
200~250
Slightly stronger, but 40N/m2 strength increase after baking. Suitable for doors, fenders, hoods, pillars.
B. Low Strength Ultra-soft Steel
INTERSTITIAL FREE STEEL
􀃎 Ti and/or Nb additions
combined with interstitial C
and N to form stable TiC, TiN
or NbCN precipitates
130~150
For difficult autobody panels of complex geometry. Suitable for automobile outer panels, oil pan, high roof panel, etc.
Laser textured steels, and new coatings such as nickel zinc are ensuring better paint finish and corrosion resistance respectively. Galvanised steel panels that provide better corrosion resistance are used to the extent of about 40% or more in a modern car body. Surface texture and coating provided by steel manufacturers demand stricter quality assurance at stamping stage. Dents and damage caused in stamping requiring repair by grinding or any surface deteriorating methods, may take away the basic advantages of special texturing. Fig. 5.3 shows the typical panels manufactured out of galvanised steels.
An intensive research and development are going on for alternate materials, manufacturing processes and stamping tools for sheet-metal components with the main objectives of cutting down the weight and unit cost of the vehicle. Simultaneously, the steel content of the car is falling with the use of aluminium and new materials, such as plastics. Aluminium may provide the most sought after solution to reduce the weight of the vehicles. A reduction of 30% in weight is achievable if the same strength, stiffness, and stability of the component are to be realised by substituting steel with aluminium. Possibility of significant reduction in die cost will be another advantage with aluminium. However, problems related to strength, serviceability, manufacturability, and above all the cost, require effective solutions before the acceptance of aluminium as a substitute to steel for body panels. Plastics for bumpers,
Fig. 5.2 High Strength Low Alloy Steel Panels in a Car Body
Fig. 5.3 Galvanised Steel Panels in a Car Body
facia, radiator grilles and even fuel tanks have become almost universally acceptable. Other applications will be commercially possible in years ahead.
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STAMPING PROCESSES
Stamping processes to be used for a panel depend on its design. However, normally the processes used extensively are blanking, drawing, piercing, forming, notching, trimming, hemming, etc. Blanking prepares the initial approximate form of the part in flat sheet. Drawing is generally the first operation to attain depth related form. Piercing, notching, hemming, are product design related operations. Trimming generally removes the extra material on the periphery of the panel provided for blankholding during draw operation. Decision on trim line is very important and becomes deciding factor to obtain good draw.
BLANKING FOR PANEL STAMPING
Press blanking uses dies specific to the part and is necessary if the shape of panel demands the same depending on part design, or if the volume of production justifies. Presently, the blanking lines operate to produce more than 60 pieces per minute. For quite some panels, rectangular, trapezoidal, or slightly curved shaped blanks may be sufficient and can be produced by shearing machines or line. Oscillating shear is a development used for flexibility in blank preparation with a stroke rate of more than 100 per minute. So, a single shearing and/or blanking line may cater to several press lines. As the coils provide the overall economy, a blanking line includes coil handling, decoiler, flattener/leveler, feeder, blanking press, and stacker for blanks. A corrective leveler is used to remove:
1. ‘Fibre’ length differentials from one surface of the strip to the other, such as coil set or cross bow.
2. ‘Fibre’ length differentials from one edge of the strip toward the centre and then to the other edge such as edge wave or centre buckles.
With gradually reducing batch size, the coil may have to be withdrawn before it is entirely used. A system to automatically take care of the situation and to resupply of the left over coil again in a fully automatic blanking system requires an effective solution.
TAILORED BLANKS
Tailored welded blanks for complex panels are being prepared through different joining processes - laser welding, spot welding, or mash-seam welding that result into a lot of material saving and better strength. Two or more pieces of same and different materials or gauges are welded into a single blank prior to stamping. Use of costlier materials such as thicker, stronger, or coated stock can be limited to just where it is required. Separate stampings of costlier material followed by welding could have meant multiple dies, multiple operations, assembly and checking fixtures. Thin or thick or different strength combinations, result also in weight reduction. In a stamping of a motor compartment rail, the original plan was to manufacture it out of 2 mm thick stock across its entire length. After a finite element analysis, it was decided to use two blanks comprising of 0.8 mm for the front part of the rail and 2 mm thick for the rest portion. It resulted in unit blank weight saving of 3.4 kgs. in purchased galvanised steel and 1.3 kgs. saving in vehicle weight with no loss of rigidity or safety aspects. Splitting the complicated panel in more than one piece may also improve nesting and consequential better yield from the coil stock. Even with addition of laser welding of the two halves prior to stamping, saving may be in million for a mass produced panel for an auto manufacturer. In a door inner, the 0.81 mm and 1.83 mm thick galvanised pieces eliminated the need for hinge and mirror reinforcements and in place spot welding. Fourteen
dies, weld fixtures, and check fixtures were also eliminated. Tailored blanks may cut down the tolerance stack and improve a car’s dimensional accuracy. A conventional door inner assembly’s dimensional accuracy covers tolerance in the thickness of steel and tolerances associated with stamping, piercing, and spot welding reinforcements. With elimination of reinforcements, the accuracy is improved. With laser welding of blanks, the dimensional variation of hole location in door panels in one case was reduced from +/- 0.5 to +/- 0. 075 millimetre. For the body side panels of Toyota model of cars, 5 straight-cut pieces of mild and high strength low alloy galvanised steel were laser welded. The blank periphery and door openings were then cut to the shape as shown in Fig. 5.4.
A HSLA steel 1.02 mm 20/20 galvanised coat thickness
B HSLA steel 1.02 mm 45/45 galvanised coat thickness
C HSLA steel 1.02 mm 45/45 galvanised coat thickness
D MS cold rolled steel 0.76 mm 45/45 galvanised coat thickness
E MS cold rolled steel 1.02 mm 60/60 galvanised coat thickness
Fig. 5.4 Tailored Blank Of Toyota Model Body Side Panel
Although material yield was reduced from 65% to 40%, the number of dies required was reduced from 20 to 4. Reinforcement elimination, weight savings, and improved aesthetics (no spot welding on door inside) were the additional advantages.
Seam welding (fenders of Ambassador model of cars in India uses seam welding for blank preparation) or spot welding is also used. However, for preparing a tailored blank, laser welding blanks provide three distinct technical advantages:
• The narrow weld seam on galvanised sheet enables corrosion resistance throughout the heat-affected zone.
• Ductility is greater compared to other welding process.
• A laser weld seam is stronger than the base material. Moreover, it results in a smooth joint between the blanks that minimises die wear in forming.
However, the tailor blanks demand stricter control of the edge quality and butt-joint pressure and other laser welding parameters such as power, welding speed, assist gas flow, beam alignment, and depth of focus, etc.
Mash seam welding is a form of resistance welding where blank segments are overlapped slightly, driven between two electrode wheels under pressure, and welded by electric current. The process is another method that can be used to prepare tailored blank. As the overlapping blank segments may vary in thickness, plannishing wheels usually follow the
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welding electrodes to cold work the welded joint to less than 10% over the original thickness. The mash seam welding is used for longish panels. At Volkswagen, the L-section members that constitute front chassis rails, are formed from mash seam-welded blanks. The blank for one member comprises three pieces of different thickness, the other four. Besides other advantages, the process improved crash ratings and merited reduction in insurance premium.
Auto-manufacturers have accepted scrap levels of 40% or more as standard due to the technical requirement for blank holding stock in draw operation or best nesting of parts on a coil. Tailored blanks can make the difference. Tailored blanks are destined to growth in the cost conscious automotive industry. As per a supplier of laser welding systems and laser welded blanks of U.S.A, saving due to tailored blanks for the auto industry can total upto $152 per car, or $ 1.47 billion per year (1994 USA production)
MAIN PRESSING OPERATION STATIONS
Main goals of the car designer and production engineer or die designers have remained as follows:
􀀹 to simplify the panels.
􀀹 to combine a number of panels in one.
􀀹 to reduce the severity of draw, and ultimately.
􀀹 to cut down on the number of stations required to finish the panels.
With change in panel design and improvement in die design, the numbers of stations have significantly reduced. Presently, almost all panels require less than 5 stations. Progress in this direction over the years for a major auto-manufacturer is shown in Fig. 5.5.
DRAWING ON DOUBLE-ACTION PRESS
Drawing of automotive panels had been the most demanding process. Conventionally the deep drawn panels use double action press as the first operation in a line (Fig. 5.6). Two slides - the outer for blank holder and the inner for punch - move along the gibs installed on uprights and ensure accurate pressing. The ‘quick approach- quick return’ motion curve of the outer slide ensures better productivity. The blank holder clamps the blank between the draw ring and the hold-down unit and is decisive for the quality of the draw. If the hold-down force is too low, the blank will develop wrinkles in the flange of the drawn parts. If the hold-down pressure is too much, the metal does not yield sufficiently in accordance with the frictional force, and tears. The optimum hold-down force is also dependent on the local behaviour of the material. Varying draw conditions in different portion of a complicated panel cause the hold-down force to vary along the contour of the part. The difference between the smallest and the greatest permissible hold-down force is a measure of the difficulty of the part so far draw is concerned. Tool builders try to adjust the local hold-down forces by the rigidity of the die, and the suitable draw beads in the blank holder. Individual motorised adjustments of the slide of the double action press permit corner or side pinch or grip control of the blank that are to be optimised for quality draw.
Fig. 5.5 Reduction in number of stamping operations
MOTIONCURVE OFINNER SLIDEMOTIONCURVE OFOUTER SLIDE0 90 180 270 360EFFECTIVEDRAW DEPTHSTROKE OF OUTER SLIDESTROKE OF INNER SLIDEDWELL
a. Ram, b. Binder ram, c. Draw die, d. Upper binder, e. Lower binder, f. Cushion plate
Fig. 5.6. Conventional Double-Action Draw and Motion Diagram
Some press manufacturers have installed hydro-pneumatic intensifier type blank holder pressure control device on each suspension point of outer slide. It facilitates the adjustment
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of blank holding capacity at each point individually as per the draw requirement for the panel. Using NC servo-controlled system for blank holder pressure control, optimum blank holder pressure can be freely adjusted during the draw operation. Temporary pressure of conventional blank holder may be avoided. (Fig. 5.7)
Fig. 5.7 NC Servo-controlled Blank holding Pressure Application
The necessity of subsequent turn-over for further processing of the panel on single action press is a big disadvantage for a press line that uses a double action press.. It does also mean possibility of damages during manual turnover operation or additional investment of an extra equipment for automatic turn-over.
STRETCH FORMING
Traditional double action drawing permits a controlled amount of the blank to draw into cavity. In the stretch forming technique, the blank is clamped so tightly all around that it can not draw in. Rather, it is stretched over the punch or lower die and set by the upper die. A lower blank holding-ring is mounted on a nitrogen pressure pad. It maintains a high load (about 100 tons) against the blank and upper ring while traversing downward with the upper ring. It thus prevents the blank from slipping between the draw beads. As shown in Fig. 5.8, the upper blanking ring drops to the lower holding ring, and locks the perimeter of the blank in the draw bead. Thereafter, the ring lower together to a dwell position, stretching the blank over the lower die. At this point, the upper die descends, completing the operation.
Stretch forming is being used for automotive panels providing advantages such as 15 to 20% smaller blank size, and elimination of turnover operation after the draw. The better quality results from the uniform stretch over the blank’s entire surface. For example, in conventional stamping of a hood, stretching occurs in the corners but very little, if at all, in the centre area. During stretch forming, measurable deformation occurs over the entire surface.
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Fig. 5.8 Steps in Stretch Forming
DRAWING ON SINGLE ACTION PRESS
With improved drawability of the sheet steel used for car body panels and the simplified panel design, most of the body panels can be drawn on single action press using pneumatically operated cushions (Fig. 5.9). The hold down force is created by drawing cushions and transferred to the blank in the bottom die, which clamps the edge areas of the blank and hold it through friction. Multiple cylinders create the force, which is distributed and transferred to the die via pressure pins. The cushion and blank holding forces are determined by the air pressure in the tank and the cylinders, and are nearly constant during the drawing process. However, the inherent disadvantage is due to the typical vibrations created by the impact of the slide on the pre-tensioned pneumatic drawing cushion. That can cause velocity related fluctuations in the blank holder force and inconsistent quality of the drawn panels.
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a. Ram, c. Draw die, d. Upper binder, e. Lower binder, f. Cushion plate, g. Hydraulic cylinder, h. Cushion pins, i. Die cushion plate
Fig. 5.9 Drawing with pneumatic cushion Fig. 5.10 Drawing with hydraulic cylinder cushion
With a hydraulic cylinder (single point) cushion (Fig. 5.10), the force is produced hydraulically through the displacement of the oil volume by a proportional throttle. Through a pressure transducer and controller, the oil pressure can be kept precisely within the defined limits and can be varied depending on the drawing stroke of the panel. With the development of hydraulic 4-points drawing cushion (Fig. 5.11), the hold-down forces may be transferred to the die in a way similar to the blank holder slide of a double action press. The draw force of the plunger type cylinders of the drawing cushions is transferred to the corners of the blank holder by four pressure rods during the down stroke of the slide. After reaching BDC (Bottom Dead Centre), the drawing cushion either follows the slide during return or returns after a programmed delay. End position damping by means of proportional valves ensures the soft and vibration free TDC (Top Dead Centre) approach of the cushion. A high response electro-hydraulic servo-valve accurately controls the hydraulic pressure. The draw cushion force can be controlled as needed during the drawing operation. The pressure of the four cylinders can also be adjusted independently. It makes the blank holder forces individually controllable over the entire drawing operation on each of the four corners of the die. The short response time for pressure changes helps in optimising the drawing operation. For example, a momentary increase of the blank holder force can initiate a stretch draw, or the material flow
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may be influenced by increasing pressure in sections of the die. Pressure pins, if directly applied can cause some drawing errors if they are not maintained to exact lengths or get elongated through wear or overloading, or by deposits between the contact surfaces. So, the cushion force may be introduced through a frame into the blank holder of the die over a larger surface, simulating the condition in a double-action press.
DIRECT INDIRECT
Fig. 5.11. Hydraulic Four point Cushion
Possibility of malfunctions caused by pressure pins is eliminated, but die builder is to work under the constraints of the frame. Advantages of the hydraulic 4-point drawing cushion are:
􀃎 Blank holder pressure may be precisely controlled and is not influenced by stroke rate related vibrations.
􀃎 Drawn part of the same consistent quality can be produced on single- action presses as on double-action presses
􀃎 Stresses on the die, drawing cushion and press are substantially reduced compared to the pneumatic systems resulting in less downtime, longer service life and less noise.
A hydraulic cushion with 15 single individually controllable pressure points (Fig. 5.12), has made an optimum forming process possible. The drawing force can be changed stepwise on each pressure point during the drawing operation. It provides the high degree of flexibility in configuring the blank holding forces along the contour of the drawn part and over the effective drawing stroke.
NC cushions, Fig. 5.13, incorporated with various transfer presses are the further developments. During the pressing, a servo valve controls the pressure exerted by the die
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cushion. The optimum load pattern is precisely ensured, so the wrinkling and cracking are prevented. Optimal load patterns are attained through numerical control, stored in memory, and reused in next setup.
Advantages of NC cushion over air cushion are:
􀃎 Better result even with sheet steel of poor drawability
􀃎 Improved finished shape such as sharp corner, convex surface and possibility of elimination of re-striking
􀃎 Reduced thickness variance of drawn panel
􀃎 Less machine trouble and better die life due to reduced impact
Fig. 5.12 Hydraulic 15-Point Cushion
Fig. 5.13 Schematic Diagram of NC Cushion
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PRESSES FOR AUTOMOTIVE PLANT
Mechanical presses are preferred in mass production for speed. By design, these presses are very fast. One press line can produce a number of panels.
TANDEM PRESS LINE
The line does not envisage any intermediate storage of panels between the presses. One double-action press for the first draw operation and 3/ 4/ 5 single action presses for such as trimming/ piercing/ flanging/ restrike, on basis of the sequence decided by the part design constitute a line. Part feeding, transfer, and unloading of the panel between the presses may be manual, semi-automatic or fully automatic (Fig. 5.14).
Fig. 5.14 Different Automation Levels for Tandem Press Lines
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In semi-automatic version, the unloading from each press is automated with consequential better quality standard of the panels in comparison with a manual line. For quality and productivity, the fully automatic press line is naturally the best solution. For low or medium volume production, where each press line is used for many types of panels and investment is to be limited, a tandem press line is recommended. Advantages are:
􀃎 The construction and controls are simpler, naturally simplest for the line with manual transport, but quite sophisticated for fully automated line
􀃎 The stamping process can be easily planned for any number of operations required for a particular panel (without stopping the press)
􀃎 Panels of any shape can be transported without difficulty
􀃎 There is no need to stop the whole line when one press is out of order
􀃎 Dies are of traditional design
􀃎 Manpower requirement for tool change is minimum in manual, but very high in fully automated line
􀃎 Output for manual and semi-automatic line remains same and the lowest. The work-force requirement for the semi-automatic line with unloading by mechanical devices is almost half of that for the manual line, where it is the highest. Output of an automatic line is higher, and require the fewest numbers of persons to operate among the three versions.
􀃎 Additional conveyor and other devices are to be provided for the panels requiring less stamping operations in a fully automated press line. A turnover device is part of the automatic press line.
􀃎 Cost of the fully automatic line is obviously the highest, and so also the space requirement.
On a fully automatic tandem press line, the maximum number of strokes per minute is about 4 to 8. Man power is used only for supervision or inspection. For a manual press line, the maximum number of strokes used per minute varies. Depending on work culture of the plant, the effective SPM may be between 2-4 or even lower. The work force requirement per press may be 2 to 5 increasing with panel size, and additional manual operations such as, oil application requirements.
TRANSFER PRESS
Conventional tandem lines have recently given way to Transfer press system. Several stations or tools are mounted in one large integrated press to complete all operations. All in-press handling of panels is automatically executed by positive-action cams with drives from the main press or through independent drives synchronised with the stroke of the press. Large panel transfer presses in two-axis or three-axis versions have revolutionised forming technology in recent years. Generally, 10 to 30 different panels may be run on a transfer press with production lot sizes ranging from 3000 to 10,000 body panels.
Main advantages of transfer presses over the automatic tandem line are:
􀁺 Integration of several operations in one press
􀁺 Higher output rates through single action draw stage, omission of turn- over operation, short transfer distances in the workpiece flow, and so effective production rate 15 to 18 parts per minute or more.
􀁺 Compact design with less space requirement
􀁺 High change over flexibility for smaller batches through fully automatic die change with a change over time of about 5 minutes or so.
However, the disadvantages remain as follows:
􀁺 Higher die cost
􀁺 Fault in one stage stops the entire process
􀁺 Limitation in part variety on one press
􀁺 Demanding training requirements for operation and maintenance
􀁺 High capital investment to the extent of about 1.5 times higher than the tandem automated press line.
Many variants of transfer presses (Fig. 5.15) are possible and have evolved, mainly based on the requirements from auto manufacturers.
DA. Double action, SA. Single action, T. Turnover, F. Feed bar, U. Updraw, C. Cushion
Fig. 5.15. Some Variants of Transfer Presses
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VARIANT - A has a combination of double action drawing press, turn-over station and tri-axis transfer press. Working speed of turn-over and synchronisation of the two presses restrict output that may be about 12 panels per minute.
VARIANT - B has a double-action updrawing station integrated in the transfer press itself. Turn-over is eliminated, as drawing takes place from below (Fig. 5.16). Bottom drive adds to the cost and a second pair of upright is also required. Drawing station may have to be preceded with some equipment to change the blank to a shape such as bending to provide with adequate positional stability. Possibility of dirt sucking during down stroke of draw punch may create quality problem.
Fig. 5.16 Updraw System in a Transfer Press
VARIANT - C has a single action draw with the aid of cushion. The blank holder forces are transmitted from the required number of individually controllable cylinders directly or indirectly to the blank holder of the die. For part height upto 250 mm, the quality of draw is comparable provided the slide speed in the working range is reduced by a linkage drive. Four-upright will be advantageous if the tonnage required in the first stage is high compared to that in subsequent stages. With multiple stations under the slide, inclination of dies may be caused at the first station.
VARIANT - D has 3-upright with individual stations distributed over two slides, thus eliminating one upright, one set of moving bolsters and one idle station and consequential shorter gripper rails.
VARIANT - E has two uprights and a single slide. Part configuration (length to width) is deciding factor. Shorter transfer step reduces the moving masses of slide and transfer mechanism. Output may be as high as 30 parts per minute.
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VARIANT - F has a single slide for each forming station, based on the principle of the tandem line with presses arranged one after the other. While the modular construction comprises of single slides, crowns, uprights, and beds, all link drives are connected via intermediate gears and couplings with the press main drive. Flexibility is enhanced with universal stations between the uprights. The variant provides the advantages as follows:
1. High degree of on-centre loading, as the undesirable interaction of the die stations due to cocking or deflection is eliminated
2. Reduced slide deflection since each slide has 4-point suspension.
3. High degree of guiding accuracy and better parallelism between bed and slide due to, 8-way guiding, small distance between uprights and tie rods in feed direction, a relatively large guided length, and direct absorption of horizontal forces by the uprights.
4. Minimal bed and slide deflection
5. Individual adjustment of shut height, press force and overload protection of each slide and thus each die station.
6. Better access to dies, clamps, and toolings on transfer and universal stations.
7. More room for scrap chutes
8. Flexible positioning of the panel possible and thus better die adaptation and simpler dies.
All these result in better part quality, improved die life, increased output, and higher overall efficiency compared to other configurations.
For variants C, D, E and F, micro-processor controlled drawing cushions are being used. The drawing results of panels are same as that achievable with double-acting presses even with complex draw requirements.
As mentioned earlier, the auto-manufacturers are trying to reduce the number of stations (dies and idle stations). It will reduce the probability of mishandling through reduction of the frequency of pick-up/ release of panels. Accessibility and visibility of the die areas in transfer presses are considered at the development stage for ultimate press efficiency.
With larger transfer press, it has become possible to stamp complex sheet metal parts in single piece that were earlier fabricated by welding of number of smaller and simpler parts. The glaring example today is that of body side panels that are now stamped in one piece. It has significantly improved the accuracy of parts and the overall quality of vehicles such as gaps and levels of doors. The same press may be used for the manufacture of multiple parts and separation in last operation such as right hand and left hand doors simultaneously (side-by-side, or one-after-the-other).
FEATURES OF A MODERN PRESS
Many features have been added to presses to improve productivity and quality as well as to make them more flexible to adapt to lean manufacturing. Features such as, self-propelled moving bolsters, automatic slide and stroke adjustment, automatic slide and bed clamps, and many similar ones, have brought down the time required for setup change-over from one panel to another. Die life is significantly affected by the stiffness of the press frame. Minimum values of the vertical spring constant and the constant of tilting (as per the DIN 56 189) guarantee optimum performance of the press. The constant of tilting of the press is important for the accuracy of the panels stamped. Press frame structure and the slides have been
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optimised with help of computer-aided design and techniques such as FEM (Finite Element Method). Deflection of press table under load is also being compensated by various means. One manufacturer places a special pressure pad between the press table and die. Impact absorber as integrated in many presses minimises the ill-effect of high impact loads (as one with stretch draw die). Improved clutch/brake units provide better performance under all operating conditions and also the best possible durability. The “wet” clutch and brake system have almost eliminated the need of adjustment for friction lining wear. The overload protection system employing hydraulic cushions built into the slide housings, provides both physical relief and electrical cut-out to protect the press and die from damage. Over years, every possible aspect of safety against failures causing human injury during the operation of presses has become built-in feature.
Table 5.2-Comparison of Different Types of Press Lines
Characteristics
Tandem press line-manual, w/o moving- bolster
Tandem press line- Automatic, with moving-bolster
Transfer press with moving - bolster
Total tonnage
100%
100%
60 to 70%
Total weight
85 to 90%
100%
60 to 70%
Floor space requirement
70 to 90%
100%
50 to 60%
Energy requirement
90%
100%
30 to 60%
No. of idle stations
4-6*
5-10
1-3
Transport distance
(feeding direction)
90 to 100%
100%
50 to 60%
Die adaptation req.
no**
partly
yes
Part alignment- variable
yes
yes, less output
no
Tooling cost
80 to 90%
100%
110 to 120%
Tool rebuilding cost
0
0 to 20%
10 to 100%
Press parts variety
100%
100%
30 to 50%
Breakdown of one
station
bridgeable
bridgeable, if req.
press stops
Resetting time
300 to 500%
100%
5 to 50%
Output w/o die change
40 to 70%
100%
130 to 150%
Output with 1 die change
20 to 50%
100%
110 to 120%
Manpower requirement
200 to 400%
100%
50 to 70%
Investment costs
75 to 85%
100%
60 to 80%
Part cost without
material
120%
100%
40 to 70%
* According to number of presses in the line
** Adaptation of overall height, if necessary
Eccentric gear drive replaced the crank-type presses to eliminate torsional deformation on the main pin, and to ensure positive slide parallelism. Plunger guided system, Fig. 5.17 provided further advantages:
1. The thrust forces generated by the eccentric motion are absorbed by the crown via the
plunger guide. Only the vertical forces act on the connection screw and slide. It effectively prevents the uneven wear of the slide gibs and slide adjustment devices caused by the thrust forces. It ensures accuracy of the press over longer period.
2. The enclosed crown confines the rotating gear noise and prevents dirt penetration.
Fig. 5.17 Plunger Guided System over Conventional System
Fig. 5.18 Link Drive System
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Touching speed of link-drive press is about one-half of an eccentric-gear press. So it makes the press to start with soft impact of the slide at the beginning of the draw. The overall drawing speed in working range is reduced to one third of an eccentric press. Slower and nearly constant speeds in the working range are ensured. The slide force at the start of the drawing operation is significantly higher than that of an eccentric-gear press and the transitions between the motion phases are smoother. Fig. 5.19 shows these advantageous features.
Fig. 5.19 Velocity and Force Advantages of Link Drive System
Since the drive linkages in the drawing range are nearly in straight line, torque loading is reduced by 25-30% as compared to conventional eccentric presses. Individual press elements are under less load; thereby accelerating and braking masses are less, press stopping distance is shorter, and wear on brake and clutch is reduced. With constant drive torque, the kinematic motion of the link drive produces a more favourable tonnage characteristic than a conventional eccentric drive. With the same nominal tonnage rating, a link drive press allows higher press load within the upper working range.
Advantages of the link drive presses are as follows:
􀁺 Production speeds and output may be increased without increasing the drawing speed.
􀁺 Drawing conditions and drawing results are substantially improved, and material of lower drawing properties can be used.
􀁺 Wear of the dies and drawing cushion are reduced, because of reduced mechanical shocks.
􀁺 Noise created during operation of the press is less.
In case of a blanking press, a special drive system reduces the slide velocity by 65% as compared to conventional eccentric drive. The die life is improved and noise level is greatly reduced.
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Machine controls in modern presses have become user-friendly. It consists of relay controls for the safety functions, programmable controllers and computer. Control provides various improved functions related to :
1. Operation guide system
2. Automatic die change system provides the data memory for the specific panel, and also displays the progress and time of automatic die change.
3. Diagnostics system displays the fault condition in message or graphic, monitors and indicates the poor action of each actuator sequentially, investigates the cause of fault through the expert system.
4. Maintenance management system indicates the regular maintenance items and the work done. Trends of data for vibration, temperature, pressure, etc., are monitored by analogue sensors and displayed for preventive maintenance.
5. Production management system records the production for each part, shows working efficiency report and maintains communication with the host computer.
The control system is expected to provide all assistance to protect the press elements and the tooling against overload. The control must measure, record, and plot the forming force versus time, and force vs. punch travel diagram (for, say, every fifth panel) for producing panels of consistent quality. A deviation from the established diagram must be detected at the earliest, and the counter measures such as adjustment of stroke length, should be initiated through the control system. The signals of pressure pickups should be processed through a computer and compared with a calibrating diagram. The value of force acting on the press slide should also be digitally shown on the front panel of the control system. The control system one day will be able to arrive at the best combination of parameters that control the quality of panel during stamping, to record in its memory, and to repeat the same during next setup, and if necessary, to modify the same to produce defect free panels.
HYDRAULIC PRESS IN AUTOMOTIVE INDUSTRY
In most of the press shop, 99% of the presses (particularly the larger ones) are used for other work than that for which they are originally procured. Investment for a large press makes it unaffordable to go for the best press for each panel. Cycle time of pressing operations is in unit seconds, so flexibility would be a necessity as the dedicated application keeps the press idle. Different parts even in same family may require operations demanding changes in many parameters along with the set of dies. Cost pressure is forcing to automate not only the transformation process itself, but also the loading/unloading and tool change. Decision for using either a mechanical or hydraulic press can not be made based upon a rule of thumb. For new investment, effective interactions between well-known press manufacturers and the user is a necessity for right decision making. While mechanical presses are still the more predominant in auto industry, hydraulic presses are being increasingly applied. High speed hydraulic presses have been developed to successfully compete with mechanical presses.
HYDRAULIC PRESS - DECISIVE ADVANTAGES:
1. Variable Force
􀀹 Infinitely adjustable force from about 20% of its maximum capacity
􀀹 Present force relatively constant throughout the stroke
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􀀹 Impossible to overload regardless of variations in stock thickness, inaccurate dies, or other factors
􀀹 Possible to protect dies designed for limited capacities and for various operations on different workpiece materials
􀀹 Over-dimensioning of dies not necessary (as against that with mechanical presses for maximum power of press)
􀀹 Possibilities of application of full force at any point in the stroke permits use for both short and long stroke application
On a 500 ton mechanical press, only 175 ton force is available for an operation at 127 mm up on stroke. About 1350 ton mechanical press becomes comparable to a 500 ton hydraulic press.
2. Variable Speed and Stroke
􀀹 Easily adjustable to stop and reverse the slide at any position in stroke (against fixed stroke of mechanical press)
􀀹 Variable speed- rapid advance to slow pressing speed just prior to contacting the workpiece provides: improved die life due to reduced shock loads and optimum speed for each operation and work material (and consequential high quality assurance and reduction in setup time)
3. Variable Capacity
􀀹 Bed size, stroke length, press speed and force capacity are not interdependent
(as against mechanical)
􀀹 Specially designed presses are more cost effective.
4. Other Advantages
􀀹 Fewer moving parts, self lubricating except for slide gibbing, or column bearings
􀀹 Quieter operation (if properly designed and mounted)
HYDRAULIC PRESS- LIMITATIONS
Speed is slower, if assessed on the basis of the possible number of strokes per minute. However, the number of strokes does not always equal the output. Overall productivity difference may be marginal. Improved circuits, new valves with higher flow capacities and faster response time, are also reducing the gap in production rate.
HYDRAULIC PRESSES FOR PRODUCTION LINE
For a highly varied spectrum of parts, a hydraulic press line is advantageous. With free programmability of the press parameters, the presses are easily adapted to new sets of dies. Modern presses are equipped with electronically controlled axial piston pumps, punch dumping systems, die change systems in many variants, and drawing cushions in single or multiple-point versions. The lead press in hydraulic press lines are set for double action operation. The holding force of the blank holder can be set differently point-by-point, similar to the drawing cushion, and adapted to the drawing process. The press can be used both in double action as well as single action modes with help of a coupling mechanism that enables
the ram and blank holder to be connected as one functional unit. Hydraulic press lines are presently used in low/medium volume production shops catering to larger varieties of parts.
Fig. 5.20 Steps for Turnover of Upper Die Plate on Spotting Press
DIE SPOTTING AND TRYOUT PRESS
Die spotting as well as try out can be carried out on the same hydraulic press of suitable specification. The final shape of the die is optimised by die spotting and precision manual working to match the die set. Die spotting presses (Fig. 5.20) must maintain extremely high degree of parallelism between slide and bolster plate at any slide point of the slide stroke during die spotting. It should also be able to provide precise spotting force. A turn over system for the die is incorporated in spotting press. The upper die is rotated automatically by 180 degrees, and placed on the press bed. It avoids overhead working on the upper die that is unsafe, error-prone, and time-consuming. The rotating platen is fixed on the slide by quick clamps. For rotation of the upper die, the slide travels down to rotation position. The splines of the rotating device are introduced in the platen on both sides. The slide is unclamped and locked in upper dead centre. The rotation device turns the platen together with the upper die. The slide comes down again. It is clamped and, after retraction of the splines, it deposits the rotating platen on the press bed. The moving bolster can be used for bringing the upper die out for spotting work or taking in the press.
In bigger stamping plant, a line of hydraulic die spotting and try out presses are installed to prepare dies before shipping for production run. With full control over the spotting forces, and slide speed and positions, all forming operations can be simulated so that the dies are made
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ready in optimal condition for production. The try-out line presses are also being equipped with multi-point drawing device with separately controllable cylinders in bed of the first press. With improved similarity of the tryout and production processes, the phase-in of dies will be better in mass production lines. The varying deformations occurring in dies on a mechanical press in actual forming require to be simulated. The try-out presses are being equipped with devices for simulation of slide tilting of the mechanical presses and with an active compensation device for flexible bending of the press bed.
HEMMING PRESSES
Some of the car components (such as doors, bonnets, decklids) consist of two panels such as one external panel with a matching interior panel. The joining of the two panels are executed on hemming presses with help of suitable single/multi-stage hemming (flanging) dies. The presses may be dedicated or flexible to carry out the hemming operations for number of components with die-change.
DIE CHANGE FLEXIBILITY
A lot of work has been done in stamping facilities to reduce the die change time, as it was one of critical reasons for poor productivity of press shops. Shingo’s philosophy of SMED (Single Minute Exchange of Dies) was a target set by Japanese automotive companies with Toyota as pioneer. A setup change time of four hours was brought down to 1.5 hours in 6 months. In next two months, the down time for the setup change came crashing down to 3 minutes. SMED was achieved with proper planning even on conventional presses by converting as many internal setup activities to external set up activities that can be completed before a setup change over is executed. Change over time was reduced using various techniques such as parallel operations using more workforce, standardisation of shut height, elimination of adjustment activities, one turn clamping and other mechanisation. Over the years, every aspect of die change over work has been studied and quick change over elements have been incorporated in presses, dies, and in material transfer mechanism used in press lines. The set of dies required for next setup is made ready outside the press. So the change over is then limited to die exchange, adjustment of press parameters for the new panel and its dies, clamping of the dies, and adjustment of accessories for the new set-up. The outgoing dies are pulled out from the presses, as the new set of dies is pushed in the respective presses. Various types of equipment such as swivel tables, tandem tool changing trolleys or shuttle tables are used for power operated tool changing. Dies are positioned in the presses with accuracy of about 0.8 mm eliminating manual prying and trial-and-error adjustments. Adjustments of press parameters such as the shut height, the stroke, are carried out simultaneously and almost automatically with pre-programmed data. Starting with standardisation of clamping heights of dies, presently auto-positioning clamps are being used to reduce the setup time. AC driven clamps in T-slots of the press slides find the new die with its sensors and clamp it securely regardless of shape and size of dies.
Moving bolsters with high positioning accuracy have become standard features for achieving quick resetting. The next setup dies are made ready on the additional moving bolsters for
each press well ahead of the change over schedule. Moving bolsters may be provided in a number of configurations (Fig. 5.21):
􀀹 Traveling to the front and rear
􀀹 Traveling to the front and afterwards to left and right
􀀹 Traveling to left and right
􀀹 Traveling to left or right, and afterwards to front and rear
Fig. 5.21 Various Configurations of Moving Bolster on Modern Presses
In the latest presses, the entire process of die change over starts automatically once the Auto Die Change Start button is pressed. The system includes: high speed moving bolster, automatic bolster clamper, automatic die clamper, automatic air pressure controller (The air pressure for the counter balance cylinders and die cushions is adjusted automatically to programmed value conforming to the workpiece to be stamped). Setup change over operations such as, the retraction of fingers, connections/disconnections of feed rails, adjustments of feed rail distance, are automatically carried out on transfer presses.
.
AUTOMATION LEVEL AND ITS FLEXIBILITY
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Press shop today can be a totally automated plant from material receipt to delivery of finished panels to Body shop. In fully automated tandem lines, an automatic blank feeder is integrated for first double action press. Loading and unloading of panels from one press to the next are carried out through various systems. Some use mechanical arms mounted on individual presses with a shuttle conveyor between the presses. The another system uses independently mounted robots to unload from a press and to load on the next press without any interference between the presses.
TRANSPORTATION OF PANELS IN TANDEM PRESS LINES
Automatic transfer of panels between the presses of a tandem line may as follows;
1. Pick and place shuttle devices, Fig. 5.22, that include:
􀀹 One press mounted linear or cam driven extractor
􀀹 One press mounted linear or cam driven loader
􀀹 One floor mounted part transfer
Fig. 5.22 Pick and Place Shuttle Device
2. Swing arm robot, Fig. 5.23 mounted to a slide or track (unless the presses are with special side slide bolster), with a six-axes articulated arm style robot mounted to an auxiliary swing arm seventh axis to reach large centre to centre distances of the press lines.
3. Pendulum arm, Fig. 5.24, 4-axes ( with optional 5th axis) articulated robot that uses a single pick up transfer between large press centre distances with out the robot being relocated for die change. Pendulum arm is mounted off to one side of the press line.
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Fig. 5.23 Swing Arm Robot
Fig. 5.24 Pendulum Arm
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Pendulum arm robot transfer of panels between the presses of a tandem line has certain clear advantages:
1. Installation is possible without shutting down.
2. Die change over time is significantly reduced.
3. Part quality is better because of single grip/release versus two grip/releases and part transfers
4. It requires one robot instead of three transfer devices.
5. It requires only one third of , end of arm toolings, fixtures and vacuum cups and reduced air consumption.
TRANSPORTATION IN TRANSFER PRESSES
On transfer presses, the handling of panels from station to station is totally integrated in the press system itself making it a STAMPING CENTRE. The transfer systems may be:
1. Tri-axis transfer
2. Crossbar transfer
Fig. 5.25 Tri-axis Transfer System
TRI-AXIS TRANSFER SYSTEM
The tri-axis transfer system, Fig. 5.25, picks up the panel holding it at its four corners with fingers provided on the feed rails, lifts, and moves the panel to the next station. The system consists of three kinetic elements: Feed/return, Clamp/unclamp, and Lift/lower. The
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manufacturer tries to keep the number of moving components to minimum to attain smooth motion at the desired high speed. Provisions for automatic connecting and disconnecting of feed bar are made to reduce the die change time. The inner distance of feed bars is automatically adjustable based on the sizes of dies. The fingers on the conventional feed bars are to be changed with new fingers manually inside the press. On new presses, automatic retractor may also retract all the fingers on to the feed bars on the bolster carrier. All replacement can be made outside the press.
Advantages of the tri-axis system are:
1. The press remains compact, as no special space is to be provided between the adjacent dies.
2. Higher stroke per minute is possible, as only single panel production is possible which is its limitation.
Disadvantages are:
1. The system is not suitable for handling large size panels, because of the four corners-holding causing buckling of the panel.
2. It is difficult to transfer panels of odd shape.
3. Die becomes complicated.
4. It is impossible to eliminate idle stations because of feed rail drive mechanism on the bed.
5. Accessibility to die area is very difficult.
6. Connection and disconnection of composite feed bars makes the system design complicated.
7. It results in a limitation of number of stations in one slide due to the bending of rails.
CROSS BAR TRANSFER SYSTEM
The cross bars with vacuum cups of the transfer system, as shown in Fig. 5.26, lift up the panels from the outer surface without deflecting them, and moves them to the next station.
The advantages of the cross-bar transfer system are as follows:
1. It provides a stable transfer of large size panels that are susceptible to buckle
2. It may simultaneously handle two or even more panels
3. The change over of the dies and handling accessories is easy.
4. Idle stations can be eliminated by adopting laterally shiftable moving bolsters.
The disadvantages of the cross-bar transfer is limited to the increased length, because of a space for cross bar parking between the adjacent dies (depending on whether there are idle stations or not). The transfer is driven by special cams developed with help of CAD to provide the best possible motion curve. High-modulus, carbon-fibre composite materials are used for the cross bars to provide the optimised characteristics related to rigidity, weight, and shock absorption.
However, press manufacturers have and are continuously working on minimising or eliminating the disadvantages of cross-bar/ tri-axis transfer systems through innovative designs developed with assistance of the vehicle manufacturers.
Fig. 5.26 Cross Bar Transfer System
IMPROVED VERSIONS OF TRANSFER
One of the manufacturer has developed Overhead Cross Bar Transfer System eliminating the vibration especially in the vertical direction of the vacuum cups installed on the cross bars. The vibration causes unstable and inconsistent suction while picking up the panels, resulting in poor press efficiency. Further, the panels get deformed and the vacuum cups leave marks on the surface of panels. The vibration increases with panel size with higher SPM (Stroke per minute). The lifting and lowering bars were replaced by stationary beams with sliding carriages (Fig. 5.27) in the overhead cross bar transfer system. It provides better accessibility and visibility of the dies for easy maintenance during operation. Further, the motion curve of the transfer system to feed the blank to Number 1 station of a transfer press must consider the following factors:
1. Projected size of the blank (especially length in feed direction) is greater than that of the panel after drawing or trimming. Consequently, the feed stroke to Number 1 station is required to be more than that to Number 2 and subsequent stations.
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2. The press angle available for transfer motion at station 1 is less than that for subsequent stations.
3. Since the blank is flat, lift stroke required for moving to station 1 can be less than that to subsequent stations.
Fig. 5.27 Improved Overhead Cross Bar Transfer System
Some presses are provided with heavy blank loader on the crown for meeting the above requirement. With flexibility in demand for changing the lift stroke as well as feed stroke, on the press with overhead vertical cross bar, special blank loader is not required.
Other design requirements to achieve higher productivity (SPM) from the transfer press through shake-free velocity and acceleration rate for the required stroke length and available press angle are:
• High rigidity of power transmission to transfer system
• Minimum backlash in the drive system
• Minimum moving mass
• Incorporation of device to minimise alternating torque on camshaft.
Some presses are provided with dual transfer motion, so that the stroke may be selected according to the panel depth. For sallower panel, the press can work with higher SPM with less lifting stroke.
AC SERVO DRIVEN TRANSFER SYSTEM
Latest in panel transportation in transfer presses is the application of servo motors with dedicated controller, Fig. 5.28, to provide the optimum motion requirement of variety of panels that will be stamped. It offers an unprecedented flexibility that can not be thought of with mechanical cam type transfer system. Stroke of lift and feed axes, the positions of clamps can be freely changed to provide the optimum motion for every panel.
Difference between a cam driven transfer and a servo-driven one will be as follows:
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Fig. 5.28 AC Servo Driven Transfer System
1. A wider range of panels can be produced on the same transfer press.
2. A deep drawn panel incompatible with cam driven transfer may be easily handled.
3. A wide range of transfer motion is possible.
4. Higher production speed is achieved by optimising the adjustable stroke on each axis, as well as the adjustable base angle.
5. As the transfer feed motion is independent and each axis can be adjusted individually and fast, die tryout time is significantly reduced.
6. Faster axis adjustment also reduces the automatic die change time.
7. A wide range of die sizes may be used because of adjustable pass line height.
8. The feed stroke can be changed easily without having idle stations.
9. Maintainability is highly improved, because of elimination of PTO shaft, cam box, etc.
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10. Unlike mechanical system, all the motions are smooth and stable with no effect of operation-based wear.
OVERHEAD TRI-AXIS SYSTEM (Fig. 5.29)
Fig. 5.29 Overhead Tri-axis System
Some systems have been designed combining the good features of conventional tri-axis transfer system with feed rails, overhead cross bar transfer system, and AC servo-driven transfer system. The system provides advantages as follows:
1. It is vibration and deflection free.
2. There is no limitation on number of stations in one slide.
3. Idle station can be eliminated.
4. Die area easily accessible and visible.
5. The design is simple without any necessity of system such as feed rail connect/disconnect, automatic finger retractor, feed rail support.
6. Die change is quicker and easily possible on moving bolster.
Automation in unloading and the palletisation system for horizontal and vertical stacking of the finished panels have been perfected. A schematic plan is shown in Fig. 5.30. Storage and handling of coils, dies, finish panels can all be automated.
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Fig. 5.30 A Schematic Plan of at-the-end of the Line Panel Handling System
SHEET METAL PRESS TOOLS - Dies and its Limitations for Auto Industry
COST REDUCTION OF DIES
Approximately, the cost of a set of press dies to stamp all the sheet metal panels for a model of car may be as much as Rs. 2500~ 3000 crores or so. Everything possible is being explored to reduce this cost with certain amount of trade off such as tool life. Developments in conventional soft materials of low-cost press tools such as zinc alloys, resins, etc. that used to be for few hundred panels, have led to considerably increased tool life. Some new zinc alloys are claimed to provide a life approaching 1 million pressings. Low cost tool materials can now selected for low/medium volume production, that are particularly suitable for countries like India, and other countries in South-East Asia. Besides, with the use of these low cost dies, these companies may remain contemporary permitting normal frequency of model changes in a competitive market.
DIE WEIGHT
Conventionally, the dies were made heavy and the minimum rib thickness in the design guidelines used to be far in excess of what is actually needed. Presently, all tool manufacturers are trying to design dies using computers and specific design standards to determine the stress loadings on the shaping tools. In case of complex components, the Finite Element Method (FEM) is being increasingly used to simulate the shaping process. All these efforts are resulting in reduction of the die weight and thus material cost of the dies.
In a case example, the reduction in weight of tools used to produce single piece side panels of a mid-size car was as follows:
Die Description Wt. tons, ’81 Wt. tons, ’91 %
Draw 59.2 43.0 11
Trim 28.6 22.0 14
Restrike 32.6 21.5 30
Trim 37.4 24.2 15
Flange 30.0 26.0 34
Pierce 24.0 21.0 06
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This reduction in weight was not by using FEM, but only through the experience of the designer. The tool weight was reduced by more than a third, by using a one-piece casting, by placing the ribs in accordance with the anticipated stress loadings, and by providing apertures in the neutral axis of the casting. Using present technique of FEM, the weight may be further reduced.
BEST COMBINATION OF DIE MATERIALS
Using the design-based materials for the different elements of a die dependent on production volume per year, the die cost may be reduced. In one particular case, for top/ bottom dies, and the blank holder of a double action draw operation, the materials for different production volume per year is as follows;
Production/year Material Hardness
50,000 FC 300 262 HB max.
100,000 FCD 600 192~269 HB
200,000 Special 197~241 HB
HARD CHROME PLATING ON CHEAPER MATERIAL
Considerable saving is also claimed by a process of hard chrome plating of automotive press tools. The cheaper grade of flake gray iron (typically FC 25 equivalent to GG 25 or PS 11) is used as base tool materials instead of costlier exotic alloys of nodular iron. Cost savings of upto 30% on material costs are possible. Gray iron is easily machinable giving better tool life, faster machining, and related advantages. With four to five times higher surface hardness with respect to cast iron, chromium plated dies provide a high resistance to wear and scoring that means better die life between reworking or polishing of dies. Moreover, the process improves average related down time (pimples, scoring), reduces oil usage because of improved friction characteristics, and improves rework rate and scrap rate because of improved formability.
LEAD TIME FOR MANUFACTURING
The development work of a production tool from the stage of component design is very much time-consuming. The total development time for a set of dies to produce one panel with conventional method, manual finish grinding for matching through spotting is approximately 12~15 months. Considering the number of sheet metal dies required in a car, the time required to tool up for a new model is critical and all efforts to reduce the same are the subject of research. Methodology used today is simultaneous engineering, where the product engineers as well as the manufacturing engineers work closely to ensure all avoidable delays. CAD (Computer aided design) data have reduced die design and development time and also the time for final trial and error final modifications. Various software that simulate the stamping processes such as deep drawing or stretch forming reduce lead time and reliance on physical proto-typing. Computerised sheet metal forming analysis simulates the friction forces between blank holder, sheet, and die during stamping, taking clamping pressure, sliding velocity, and sheet orientation into consideration. Modeling die elements, say various drawbead sizes on a computer rather than in the prototype shop saves significant time in tool design. Software vendors and the auto-manufacturers are developing complimentary systems to act as a fully associative package. Pro/DIFACE from Parametric technology Corporation and OPTRIS from Matra Datavision are two such examples. With Pro/DIFACE, an engineer creates or imports a surface model of car hood (for example), and defines
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specific regions of the die face and related features such as blank holder, part addendum, and trim lines. Designers can then generate solid models of punch, die cavity, and die components. The Pro/DIEFACE program allows users to also define a press direction coordinate system with translation offsets and rotation angles. Any changes automatically alter part features defined in relation to press direction. The program also provides a contour map showing distribution of the punch contact area, and expansion ratios of various section lengths before and after forming. OPTRIS is another such metal stamping simulation program from Matra Datavision that runs alone or with EUCLID family of CAD/CAM products. Inputs are a part drawing, method plan, blue print of the drawing die, and CAD data for the workpiece. The program creates a numerical model of the bottom die, then offsets a portion of this surface to create the punch. Using IGES as a standard translator, the tooling surfaces are transferred to the CAM environment to establish milling tooth paths and define finite elements for die components. Finite element geometry is then translated into a neutral format and exported to OPTRIS, which defines mechanical and kinematic information for nodes and elements to do the stamping simulation. The resultant data indicates the likelihood of breaks, creases and shape defects in the drawn part.
The possibility of tilting and rotation (about z-axis) of press slide and the upper die with respect to press table affects the performance of the drawing and cutting tools. The effective alignment of the press slide and the upper die with respect to the bottom die is ensured generally through two types of guidance system: Pillar Guides, and Heel Blocks. Diameter of pillar guides is critical to bear the moment of slide tilt during operation. The mismatch between the upper and lower die is reduced with increasing the diameter of the pillars and the quality of panels produced gets improved. Increase in guidance with heel blocks can be attained with increase in guiding surface area. However, the combination of pillar guides with heel block guides provides only marginal improvement of guidance behaviour.
COMPUTERISED DIE MANUFACTURING
CAD has also eliminated a number of manufacturing steps that were used in conventional die manufacturing. Fig. 5.31 shows a flow chart for die development using CAD and CNC machining.
The CAD data can directly be loaded CNC die sinking machine. Advantages are:
• More accurate machining compared to mechanical copying
• Workpieces produced directly by NC milling can be accurate within 0.2 mm compared with an average of 0.6 mm with copy milling
• Elimination of cumulative inaccuracies due to use of copying masters
• Elimination of dimensional variations on large masters due to the effect of temperature
• Manual finishing reduced by upto 50%
CNC machines are provided with automatic tool changer facilities to complete all operations in single clamping, after the machining of the reference surface. Total die making time in man-hours can be reduced by 30% or more. With a 3-axis machine, the direction of the
Fig. 5.31 A Flow Chart for Die Development Using CAD and CAM
milling cutter axis can not be changed. The effective cutting speed at the centre of the ball-nosed cutter becomes zero. The 3-axis milling requires the tool to remain parallel to its axis. It
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results in a poor surface finish on the die, causes heavy cutter wear, and requires long machining time. A better tool material can not be used effectively.
Today, a 5-axis machine is preferred for the reasons as follows:
1. 5-axis milling permits use of an end mill rather than rounded cutter for higher metal removal rates and better surfaces
2. With 5-axis milling, the tool remains perpendicular to the workpiece surface. It is possible to space the cutter paths more widely apart for a given peak to valley groove depth.
3. Time of manual finishing is drastically reduced.
4. Parts with overhanging edges can only be machined with 5 axis control, since the control is otherwise inaccessible.
5. Tilting the tool relative to the workpiece surfaces additionally increase removal rates, since the tool need not cut at its centre, where the removal rate is near zero.
Fig. 5.32 A 5-Axis Cutter Head
However, the 5-axis milling provides the advantages only in machining of convex surfaces with slight curvature, for example exterior panels of modern car such as roof, bonnet. A 5-axis cutter head is shown in Fig. 5.32
HIGH SPEED MILLING
Presently high speed 5-axis machines are preferred for copy milling. The machine with conventional control, if run at higher feed rates, provides reduced accuracy, as servo errors are proportional to the square of the feed rate. High speed machining requires high speed feed control unit. The feed control unit reads NC data in advance, calculates the effects of inertia and servo response on tool path at the desired feed rate, and issues new data to compensate the error. Even the feed rate is optimised through special features in control so that the dies with varying form can be machined without gouges and overshoot drops. The
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ball nose end mill produces a finer finish, or smaller peak-to-valley or cusp height, as the stepover or lateral feed becomes smaller. The finer the surface finish, the less time is needed for the final polishing cycle. High speed milling can reduce finish milling time by a factor of five. However, the main objective of high speed milling is to minimise or eliminate bench finishing or hand finishing that represents about 25% to 38% of manufacturing time for a die. It may reduce highly demanding human skill that is very much in short supply today. Bench finishing is also a source of geometric error of the die profile. The manual grinding can not be controlled as precisely over a profile as much it is possible with a programmed tooth path on a CNC machine. It may result in rework at tryout stage. High speed milling has reduced the time required for manual finishing and tryout as shown in Fig. 5.33.
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HIGHSPEEDMILLING MACHINEINTRODUCEDEFFECTACHIEVEDBY IMPROVEDMACHININGACCURACYDATUM FACEMACHININGPRIMARYMACHININGASSEMBLY/MACHININGPROFILE MILLINGROUGHINGMODEL FITTINGPREPARATIONSFOR DIEMATCHINGDIE MATCHINGPART ASSEMBLYGENERALASSEMBLYINSPECTIONELIMINATED(36 %
OR MORE)MACHINING MAN HOURSFINISHING MAN-HOURSDIEMAKING MAN-HOURS
Fig. 5.33 Man - Hours Reduction Due to High Speed Milling
LASERCAV - a new production method
Lasercav process is the latest in die manufacturing methods with a lot of possibility for future development. In the process, a light beam is focused to a width of a few tenths of a millimeter cuts away the material line by line. The thickness of the layer of material removed is determined by the process parameters (e.g. laser power, feed rate). A roughing or a finishing operation can be selected, just as with milling. Machines are being developed both in vertical and horizontal versions. However, to enable greater accuracy than what has been achieved, the emphasis is on development of a Lasercav programming module and depth sensors. Lasercav very soon if not replace, will effectively supplement conventional stock removal processes. Besides, it will enable dies to be produced from materials that have hitherto been unmachinable or are difficult-to-machine.
DIE FINAL FINISHING PROCESS
For finishing of dies, both rigid grinding wheel or stone as well as flexible disks have been used- each with certain advantages and disadvantages. Main objective all the time in the process is to flatten the cusps top so that the groove bottoms remain untouched. Fig. 5.34 shows surfaces (magnified) as obtained from copying, and one after an undesirable grinding and finally one after an ideally grinding. Some of the major die manufacturers have developed robotised die polishing machines. The process uses a closed loop force controlled robot with a flexible grinding disc. Alternatively, a flexible pad with abrasive holder movement simulates human wrist movement with a continuous measurement of the heights of the cusps till it reaches desirable value. Basically, the bottoms of the grooves represent the desired final surface if the cusps can be perfectly matched to the surface. It has further reduced the manual finishing that becomes limited thereafter, to only the inaccessible areas of the robot hand and the tool used.
Fig. 5.34 Surface Characteristics after Milling, Poor, and Correct Manual Grinding
STANDARDISATION OF DIE ELEMENTS
Another possibility to reduce the development time comes from the design of dies using modular-type composite tools and plug-in modules. A segmented, form-related tool is constructed on a standard base matrix that is configured as a die set. By the use of standard segments and combination thereof, a die set can be manufactured with lowest lead time.
NEW AREAS - LASERS FOR TRIM /PIERCE
Laser cutting machines with 3-axis, 5-axis movements are finding application in sheetmetal component manufacturing and are being used to do number of complimentary operations. Biggest advantage is its flexibility and the torch path can be changed as per the component
42
43
design and manufacturing requirements. Blanking, piercing, trimming, notching can be easily performed for varied components. With improved cutting speed, the time cycle achieved may be viable for low volume requirements. The laser may be the most efficient manufacturing technique for the smaller holes in odd positions because of its flexibility. Generally, the punch life becomes critical or die design becomes complex. A number of additional dies may be required. The process may be easily integrated in the existing manufacturing system to increase production and efficiency, and to cut down tooling, maintenance and setup cost. For holes with less than 2:1 hole/thickness ratios, laser provides the best solution. For components such as doors, bonnet or decklid with complex holes and contours, a laser system may improve part quality and reduce production cost.
As the panels are being designed mostly using CAD system, CAM software can develop the laser working program for the process by starting from the description of component geometry. Teach mode program that may be time-consuming and may require skill, may be replaced by the CAM software. Laser cutting is destined to get effectively integrated in stamping plant for automotive components. 5-axis laser cutting machines are already being used for all trimming and piercing operations particularly for low/medium volume operation such as proto-typing or after sales market requirements. The laser cutting speeds based on material thickness may go upto 10 metres per minute for 3-axis cutting. On 5-axis machines, cutting speed of 5 to 6 metres per minute are reached depending on the part geometry of the body panels. Even zinc coated sheets can be cut at 4 metres per minute. Laser capability to combine several processes such as cutting, shearing, and welding into one work station will provide immense opportunity to improve overall part quality, and will ultimately reduce product cost.
SOME NEW APPROACHES IN METAL STAMPING
New methods are being developed to reduce the number of steps as well as to cut down the tooling cost and its development time. The Toyota Flexible Press System is a similar approach for small-lot production, which is becoming the trend and that is expected to grow faster in coming years. The system consists of three major processes:
1. drawing performed by a newly developed liquid-pressure press-forming method,
2. trimming with a high speed 3-axis laser cutting machine, and finally
3. cam flanging by multi-directional press forming method in which the pressure is simultaneously applied from six directions.
Five step process for a fender was reduced to 3 step process (Fig. 5.35)
A significant step is being taken to manufacture panels with a “resilient” tool half, only one tool half specific for the product must be produced. Forming metal with a rubber pad (known as the Guerin principle), as shown in Fig. 5.36 is one such method. The rubber pad is traversed towards the tool with the sheet metal panel lying on it. The rubber pad thus makes contact with the tool under increasing pressure thereby forming the sheet. The higher the pressure chosen, the more uniform becomes the vertical pressure distribution along the tool side wall. Recesses can thus be filled and spring back together with any manual second operation work may also be reduced.
Fig. 5.35 Toyota Flexible Metal Forming System
Fig. 5.36 Principle of a Rubber Pad Press
44
In another system, Fig. 5.37, the rubber pad is replaced by a rubber diaphragm to which oil pressure is applied thereby bringing the metal panel into contact with the tool contour. Pressure distribution is somewhat more homogenous and somewhat greater drawing depth can be achieved. The processes still require fine tuning for effective application in medium volume production.
Fig. 5.37 Principle of a Fluid Cell Press
PRESS SHOP MANAGEMENT
A press shop is characterised by extremely high capital investments making productivity target as high as possible a necessity. The objective always is to obtain the longest time period of press producing good parts. In a press shop, each period that is longer than the time for a press stroke and that has not led to production of a good part is to be regarded as down time. A typical delay analysis of various operations of press shop provides the data as follows:
Change over time - die change 7%
Unproductive time- trial pressings 12%
Organisational idle time 3%
Machine downtime 13%
Technical idle time- die failure 7%
Effective useful time-press time 58%
The table above is good enough to show that the impression of press stoppages being caused exclusively by the die change is not correct. However, as explained earlier, a lot of work done in area of reducing setup time has brought down the loss time in setup change to SMED level. Data below shows the significant improvement in die change time between 1978 to 1992.
Reduction in Die Change Time over the Years
Time, minutes
Die Change Elements 1978 1979* 1992**
1. Die transportation 3.2 - -
2. Die Setting 4.0 1.8 0.36
3. Waiting for crane 6.0 - -
45
4. Cushion pins setting 1.5 - -
46
5. Slide adjustment 1.5 - -
6. Adjustment for automation 2.3 1.8 -
7. Conveyor setting 1.5 0.5 0.09
8. Preparation for blanks and pallets 2.0 1.5 0.12
9. Preparation for tool setting 1.2 0.9 -
10. Trial Stamping 3.3 2.0 -
________________________________________________________________________
Total 26.5 8.5 0.57
________________________________________________________________________
* Effect of Quick Die Change System
** Effect of Kaizen
Ways and means to arrive at SMED is known to all through printed materials available on the subject. Perhaps, it will be other areas such as unproductive time in trial pressings, and maintenance of machines and toolings that require careful manufacturers’ attention. A process monitoring that indicates a trend statement concerning the parameters controlling the forthcoming faults, will be desirable to prevent the faults as against the present ones that indicate them only after they have occurred.
New technologies for presses, systems, transfer arrangements and stores have been brought in for ‘Just-in-Time’ production system. Even with in-house stamping facility, unlike machining, the ‘Just-in-Time’ in its true sense is not possible, because of the basic nature of the machine speeds and change over limitations because of dedicated toolings. Effort can only be made to reduce the batch sizes to reduce the inventory/ stock levels of raw materials in circulation and number of finished pressings to a practical minimum level. Some stamping shops are producing the batch sizes that will be sufficient for only 2 to 3 hours in assembly.
An efficient and computerised production control and planning system for requirement-based and capacity related production control is essential for stamping plant. The magnitude of investment in a new press shop requires optimisation of capacity created. All stages of the press shops- from the coil stores to the finished part store-are being optimised. With high level of automation, the press shops may be justified for 24 hour operation through seven days a week.
The basic approach to press shop management is clear from a recent report from AUTOMOTIVE INDUSTRIES: GM’s 13 North American stamping plants have 57 different press configurations. A standardisation programme would reduce that to six either through reconfiguration or total elimination. GM plans to run all its press lines 24 hours a day. The press lines will all have common controls and material handling systems, common end-of-line part handling. “The presses are old and obsolete” should not become the excuse for not achieving the desired productivity. Presses are high cost investment and require very carefully planned and effectively implemented maintenance based on Total Productive Maintenance philosophy. The services of experts, specialised maintenance groups, or original equipment manufacturers may be sought for further improvement of productivity. Planned maintenance and timely repair will be essential to maintain the desired accuracy levels. A rebuilding will be essential to upgrade even a press line of very old technologies. The desired level of productivity may be achieved through retrofits in presses, die change over system, and the panel transfer system. In some of the world’s best car manufacturing plants, even 30~40 year old press lines are producing the panels for the latest cars. It has been possible only with good maintenance and upgradation to incorporate the latest innovations.
47
With the progress in technology, the presses are sufficiently flexible to accommodate dies for any new product. However, the development time as well as manufacturing time requirement for tools require some major technological breakthrough to meet the market demand.
One major aspect of the pressing systems will be the reliable automatic inspection of the finished panels. The system must have in-line facility to scan the parts contour and finish of the outer surfaces of skin panels for scratches, creases, draw marks, etc. at a speed of the production line.
With engineered blanks, laser cutting and newly developed liquid pressure forming methods, the basic processing sequence may undergo change. Manufacturing engineers will have to work hard to keep in touch with the developments in different areas. It will help them to decide the optimum effective sequences for the processing of the panels for a new facility. They may also explore the possibility of upgrading the existing manufacturing with retrofitment of new innovations.
NEW TRENDS
Competition is forcing auto manufacturers to take an all-out effort to reduce cost. In a production setup of 10,000 panels per month, approximate cost breakups under different heads are as follows:
Material cost 75%
Die cost 15%
Running cost 10%
The next generation of cars will be largely dependent on lightweight construction using steel. The majority of new approaches for weight reducing of structures are based on further development in the fields of materials (sheet qualities and semi-finished products), forming technology, and joining technology. Tailored blanks or patchwork technology, simultaneous stampings of more than one panel, change in blank shape, are the methods used for reduction in material cost. Tailored blanks contribute to lightweight construction as a result of the varying sheet thickness. Patchwork technology makes it possible to manufacture components which are matched to the theoretical sheet-thickness requirements and come very close to satisfying the main goal of weight reduction.
Work on reduction in die cost is covering various activities such as, reduction of number of dies required for each panel, reduction in size and weight of dies, and redesign of panel construction to replace number of parts by one, i.e. Body side (Fig. 5.38)
Running cost saving is coming through new press technology with increased strokes per minute, stable and high speed feeding system, improved servo-controlled drives of transfers, reduced energy consumption through optimised design, and so on. Modular transfer press is the latest that provides the best of tandem line and conventional transfer press, as the dies for the press are interchangeable with those for the tandem line. While automobile builders are gradually switching over to transfer presses (mechanical), the component manufacturers still prefer tandem lines and hydraulic presses. Single action press with die cushion is
Fig. 5.38 Body Side Panel - Divided Type Versus One-Sheet Type
replacing double action draw press. Mastering of NC cushions will result in reliable quality of panels.
Trends in stamping have highly influenced by the manufacturing concepts of individual company and the country. For example, when one Japanese company prefers a simple fixed bar type vacuum cup feeder, the another company opts for tiltable bar type feeder. European automakers prefer slide cushion, whereas Japanese prefer die cushion. Japanese were pioneer in reducing the number of work stations to four for almost all major panels, whereas Europeans’ average may still be about six per panel. Level and type of press automation also defer from company to company.
48

Friday, October 2, 2009
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DIRECTV Inc
El Segundo, California

The DIRECTV Group, Inc. is a provider of digital television entertainment in the United States and Latin America. The business segments, DIRECTV U.S. and DIRECTV Latin America are engaged in acquiring, promoting, selling and/or distributing digital entertainment programming through... more
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DISH Network Corporation
Englewood, Colorado

DISH Network Corporation is a provider of satellite delivered digital television to customers across the United States. DISH Network services include hundreds of video, audio and data channels, interactive television channels, digital video recording, high definition television,... more
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EchoStar Communications Corporation
Inglewood, Colorado

EchoStar Corporation (EchoStar), formerly EchoStar Holding Corporation, will operate two primary businesses: digital set-top box business and a fixed satellite services business. EchoStar had a spin-off from DISH Network on January 1, 2008. The Company’s set-top box business designs,... more
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Intelsat , Ltd.
Washington , Dc, District of Columbia

Intelsat Corporation is a provider of fixed satellite services worldwide and a provider of these services to each of the media and network services sectors. The Company provides service on a global fleet of 26 satellites that are integrated with 27 other satellites owned by other... more
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GlobeCast
London, United Kingdom

GlobeCast, a subsidiary of France Telecom, is the leading global provider of content management and worldwide transmission services for professional broadcast delivery. The company operates a secure global satellite and fibre network to manage and transport 10 million hours of video... more
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Telesat
Gloucester, Ontario, Canada

Telesat is a pioneer and world leader in satellite operations and systems management. The company made history in 1972 with the launch of the first Canadian commercial communications satellite in geostationary orbit. Today, Telesat competes with other top international satellite fleets in... more
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Arqiva Limited
Winchester, Hampshire, United Kingdom

Arqiva has a 50-year history in transmission and has helped pioneer the technologies of the digital age. 22 million UK homes receive ITV, Channel 4 and Five via Arqiva's national transmitter networks. The company also provides transmission for most UK independent radio stations, both... more
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Bell ExpressVu LP
North York, Ontario, Canada

Launched in September 1997, Bell ExpressVu is the largest and fastest growing direct-to-home (DTH) television company in Canada and the fifth largest broadcast distributor in the country with over 725,000 subscribers as of December 2000. Currently, the company offers more than 200 video... more
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SES ASTRA
Austin, Texas

SES ASTRA operates the ASTRA Satellite System, offering a comprehensive portfolio of broadcast and broadband solutions for customers in Europe and beyond. ASTRA broadcasts television and radio programmes directly to millions of homes, and provides internet access and network services to... more
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SES GLOBAL company

SES GLOBAL (Euronext Paris, Luxembourg Stock Exchange: SESG) wholly owns three market-leading satellite operators, SES ASTRA in Europe, SES AMERICOM in North America, and SES NEW SKIES, which provide global coverage and connectivity. The Company also holds strategic participations in... more
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Sentech
Carrollton, Texas

Sentech has been at the leading edge of communication technology, pioneering the provisioning of broadcast signal distribution services. Sentech, a commercially operated, state-owned enterprise, is the largest signal distributor for broadcasting in Africa, transmitting programs for... more
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Shaw Communications Inc
Calgary, Alberta, Canada

Shaw Communications Inc. is a communications company whose core business is providing broadband cable television, Internet, Digital Phone, telecommunications services (through Shaw Business Solutions) and satellite direct-to-home services (through Star Choice) to approximately 3.3 million... more
*
Arabsat

Backed by the 21 member countries of the Arab League, and with its 30-year heritage of continuous operations, Arabsat offers the Arab world an unrivalled range of satellite-based communications services such as Direct-to-Home Television and Radio, telephony, Internet and direct Broadband... more
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MEASAT

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Tata Sky Ltd.

Tata Sky Ltd., a joint venture of TATA and STAR, is committed to build a state-of-the-art Digital infrastructure for Pay Television in India. Tata Sky plans to introduce a nationwide Direct-to-Home (DTH) service that would allow it to reach every Indian home, however remote it may be. The... more
*
AlphaStar International Inc
Greenwich, Connecticut

AlphaStar is a 21st Century globally integrated Communications Company offering continuous full-motion high definition video, in IP multicasting and streaming formats, television and other multimedia programming services to the Internet through its uniquely positioned, high-bandwidth... more
*
Astro

Astro is Malaysia's leading multimedia broadcaster and producer of Malay, Chinese, Indian and English language programming content. It owns and operates the only direct-to-home satellite TV service with access to some 10 million viewers in over 2 million homes, representing 38% of TV... more
*
Pittsburgh International Telecommunications Inc
Pittsburgh, Pennsylvania

Pittsburgh International Telecommunications was established in 1983 as Mobile Satellite Communications, Inc. in Pittsburgh, Pennsylvania. The company provided mobile satellite uplinking services and owned and operated one C-Band transportable vehicle, which serviced the major television... more
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ProtoStar LTD
San Francisco, California

ProtoStar is an Asian satellite services operator that was formed to acquire, launch and operate high-power geostationary satellites to lease capacity to Asian DTH and broadband service providers. The technical characteristics of its satellites and the configuration of the satellite... more
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ASC Enterprises Limited
Lexington, Kentucky

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Super Value Channel Inc
Pomona, California

SVC sells a variety of consumer products through DTH satellite TV, Cable TV, and over the internet. With full-scale TV production facility and multi-lingual "TV Shopping Experts" who may speak the ethnic languages to better service the customers, SVC is capable to broadcasting informative... more
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SET Discovery Ltd.

SET Discovery Private Limited is a joint venture between SET India Pvt. Ltd. and Discovery Communications India. The company was set up in April 2002. Today, the company distributes 15 leading channels under the brand name of TheOneAlliance to over 61 million homes spread over 4000 cities... more
*
Atlanta DTH , Inc.
City Of Industry, California

Established in 1993, Atlanta DTH, Inc. is a leading supplier in the DTH satellite industry. We provide a complete product line of DTH satellite equipment such as IRD and LNBF, as well as customer-driven satellite network services and customer management system. ADTH's RV division... more
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Cyfrowy Polsat S.A.

Launched in 1999, Cyfrowy Polsat offers today 35 television channels in the Polish language and five radio channels as well as hundreds of international Free-To-Air channels. The platform also offers interactive applications, such as TV banking, weather forecasts, SMS Chat, e-mail and... more
Posted by ramkumar at 9:26 AM 0 comments
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Sort By: Relevance (Default) Company Name Ascending Company Name Descending Revenue Results 1-24 of 24 companies


DIRECTV Inc
El Segundo, California

The DIRECTV Group, Inc. is a provider of digital television entertainment in the United States and Latin America. The business segments, DIRECTV U.S. and DIRECTV Latin America are engaged in acquiring, promoting, selling and/or distributing digital entertainment programming through... more


DISH Network Corporation
Englewood, Colorado

DISH Network Corporation is a provider of satellite delivered digital television to customers across the United States. DISH Network services include hundreds of video, audio and data channels, interactive television channels, digital video recording, high definition television,... more


EchoStar Communications Corporation
Inglewood, Colorado

EchoStar Corporation (EchoStar), formerly EchoStar Holding Corporation, will operate two primary businesses: digital set-top box business and a fixed satellite services business. EchoStar had a spin-off from DISH Network on January 1, 2008. The Company’s set-top box business designs,... more


Intelsat , Ltd.
Washington , Dc, District of Columbia

Intelsat Corporation is a provider of fixed satellite services worldwide and a provider of these services to each of the media and network services sectors. The Company provides service on a global fleet of 26 satellites that are integrated with 27 other satellites owned by other... more


GlobeCast
London, United Kingdom

GlobeCast, a subsidiary of France Telecom, is the leading global provider of content management and worldwide transmission services for professional broadcast delivery. The company operates a secure global satellite and fibre network to manage and transport 10 million hours of video... more


Telesat
Gloucester, Ontario, Canada

Telesat is a pioneer and world leader in satellite operations and systems management. The company made history in 1972 with the launch of the first Canadian commercial communications satellite in geostationary orbit. Today, Telesat competes with other top international satellite fleets in... more


Arqiva Limited
Winchester, Hampshire, United Kingdom

Arqiva has a 50-year history in transmission and has helped pioneer the technologies of the digital age. 22 million UK homes receive ITV, Channel 4 and Five via Arqiva's national transmitter networks. The company also provides transmission for most UK independent radio stations, both... more


Bell ExpressVu LP
North York, Ontario, Canada

Launched in September 1997, Bell ExpressVu is the largest and fastest growing direct-to-home (DTH) television company in Canada and the fifth largest broadcast distributor in the country with over 725,000 subscribers as of December 2000. Currently, the company offers more than 200 video... more


SES ASTRA
Austin, Texas

SES ASTRA operates the ASTRA Satellite System, offering a comprehensive portfolio of broadcast and broadband solutions for customers in Europe and beyond. ASTRA broadcasts television and radio programmes directly to millions of homes, and provides internet access and network services to... more


SES GLOBAL company

SES GLOBAL (Euronext Paris, Luxembourg Stock Exchange: SESG) wholly owns three market-leading satellite operators, SES ASTRA in Europe, SES AMERICOM in North America, and SES NEW SKIES, which provide global coverage and connectivity. The Company also holds strategic participations in... more


Sentech
Carrollton, Texas

Sentech has been at the leading edge of communication technology, pioneering the provisioning of broadcast signal distribution services. Sentech, a commercially operated, state-owned enterprise, is the largest signal distributor for broadcasting in Africa, transmitting programs for... more


Shaw Communications Inc
Calgary, Alberta, Canada

Shaw Communications Inc. is a communications company whose core business is providing broadband cable television, Internet, Digital Phone, telecommunications services (through Shaw Business Solutions) and satellite direct-to-home services (through Star Choice) to approximately 3.3 million... more


Arabsat

Backed by the 21 member countries of the Arab League, and with its 30-year heritage of continuous operations, Arabsat offers the Arab world an unrivalled range of satellite-based communications services such as Direct-to-Home Television and Radio, telephony, Internet and direct Broadband... more


MEASAT


Tata Sky Ltd.

Tata Sky Ltd., a joint venture of TATA and STAR, is committed to build a state-of-the-art Digital infrastructure for Pay Television in India. Tata Sky plans to introduce a nationwide Direct-to-Home (DTH) service that would allow it to reach every Indian home, however remote it may be. The... more


AlphaStar International Inc
Greenwich, Connecticut

AlphaStar is a 21st Century globally integrated Communications Company offering continuous full-motion high definition video, in IP multicasting and streaming formats, television and other multimedia programming services to the Internet through its uniquely positioned, high-bandwidth... more


Astro

Astro is Malaysia's leading multimedia broadcaster and producer of Malay, Chinese, Indian and English language programming content. It owns and operates the only direct-to-home satellite TV service with access to some 10 million viewers in over 2 million homes, representing 38% of TV... more


Pittsburgh International Telecommunications Inc
Pittsburgh, Pennsylvania

Pittsburgh International Telecommunications was established in 1983 as Mobile Satellite Communications, Inc. in Pittsburgh, Pennsylvania. The company provided mobile satellite uplinking services and owned and operated one C-Band transportable vehicle, which serviced the major television... more


ProtoStar LTD
San Francisco, California

ProtoStar is an Asian satellite services operator that was formed to acquire, launch and operate high-power geostationary satellites to lease capacity to Asian DTH and broadband service providers. The technical characteristics of its satellites and the configuration of the satellite... more


ASC Enterprises Limited
Lexington, Kentucky


Super Value Channel Inc
Pomona, California

SVC sells a variety of consumer products through DTH satellite TV, Cable TV, and over the internet. With full-scale TV production facility and multi-lingual "TV Shopping Experts" who may speak the ethnic languages to better service the customers, SVC is capable to broadcasting informative... more


SET Discovery Ltd.

SET Discovery Private Limited is a joint venture between SET India Pvt. Ltd. and Discovery Communications India. The company was set up in April 2002. Today, the company distributes 15 leading channels under the brand name of TheOneAlliance to over 61 million homes spread over 4000 cities... more


Atlanta DTH , Inc.
City Of Industry, California

Established in 1993, Atlanta DTH, Inc. is a leading supplier in the DTH satellite industry. We provide a complete product line of DTH satellite equipment such as IRD and LNBF, as well as customer-driven satellite network services and customer management system. ADTH's RV division... more


Cyfrowy Polsat S.A.

Launched in 1999, Cyfrowy Polsat offers today 35 television channels in the Polish language and five radio channels as well as hundreds of international Free-To-Air channels. The platform also offers interactive applications, such as TV banking, weather forecasts, SMS Chat, e-mail and... more

Posted by ramkumar at 9:26 AM 0 comments
This article contains weasel words, vague phrasing that often accompanies biased or unverifiable information. Such statements should be clarified or removed. (March 2009)

Satellite television is television delivered by the means of communications satellite and received by a satellite dish and set-top box. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.

Contents
[hide]
1 History
2 Technology
3 Standards
4 Categories of usage
4.1 Direct broadcast via satellite
4.2 Television receive-only
4.2.1 Direct to home television
4.2.2 Programming
4.2.3 Broadcasting centers
4.2.4 Encryption and transmission
4.2.5 The dish
4.2.6 The receiver
5 Satellite television by region and country
5.1 United States
5.2 India
5.3 Canada
5.4 United Kingdom
6 See also
7 References
8 External links


[edit] History
The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom 2 was launched in 1963. The world's first commercial communication satellite, called Intelsat I (nicknamed Early Bird), was launched into synchronous orbit on April 6, 1965. The first national network of satellite television, called Orbita, was created in Soviet Union in 1967, and was based on the principle of using the highly elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. The first domestic North American satellite to carry television was Canada’s geostationary Anik 1, which was launched in 1972.[1] ATS-6, the world's first experimental educational and Direct Broadcast Satellite, was launched in 1974. The first Soviet geostationary satellite to carry Direct-To-Home television, called Ekran, was launched in 1976.

[edit] Technology
Satellites used for television signals are generally in either naturally highly elliptical (with inclination of +/-63.4 degrees and orbital period of about 12 hours, also known as Molniya orbit) or geostationary orbit 37,000 km (22,300 miles) above the earth’s equator.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very large, as much as 9 to 12 meters (30 to 40 feet) in diameter. The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder 'retransmits' the signals back to Earth but at a different frequency band (a process known as translation, used to avoid interference with the uplink signal), typically in the C-band (4–8 GHz) or Ku-band (12–18 GHz) or both. The leg of the signal path from the satellite to the receiving Earth station is called the downlink.

A typical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Typical transponders each have a bandwidth between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees from the next satellite (to avoid interference). For Ku the spacing can be 1 degree. This means that there is an upper limit of 360/2 = 180 geostationary C-band satellites and 360/1 = 360 geostationary Ku-band satellites. C-band transmission is susceptible to terrestrial interference while Ku-band transmission is affected by rain (as water is an excellent absorber of microwaves at this particular frequency).

The downlinked satellite signal, quite weak after traveling the great distance (see inverse-square law), is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the flared front-end of a section of waveguide that gathers the signals at or near the focal point and 'conducts' them to a probe or pickup connected to a low-noise block downconverter or LNB. The LNB amplifies the relatively weak signals, filters the block of frequencies in which the satellite TV signals are transmitted, and converts the block of frequencies to a lower frequency range in the L-band range. The evolution of LNBs was one of necessity and invention.

The original C-Band satellite TV systems used a Low Noise Amplifier connected to the feedhorn at the focal point of the dish. The amplified signal was then fed via very expensive and sometimes 50 ohm impedance gas filled hardline coaxial cable to an indoor receiver or, in other designs, fed to a downconverter (a mixer and a voltage tuned oscillator with some filter circuitry) for downconversion to an intermediate frequency. The channel selection was controlled, typically by a voltage tuned oscillator with the tuning voltage being fed via a separate cable to the headend. But this design evolved.

Designs for microstrip based converters for Amateur Radio frequencies were adapted for the 4 GHz C-Band. Central to these designs was concept of block downconversion of a range of frequencies to a lower, and technologically more easily handled block of frequencies (intermediate frequency).

The advantages of using an LNB are that cheaper cable could be used to connect the indoor receiver with the satellite TV dish and LNB, and that the technology for handling the signal at L-Band and UHF was far cheaper than that for handling the signal at C-Band frequencies. The shift to cheaper technology from the 50 Ohm impedance cable and N-Connectors of the early C-Band systems to the cheaper 75 Ohm technology and F-Connectors allowed the early satellite TV receivers to use, what were in reality, modified UHF TV tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on 70 MHz where it was demodulated. This shift allowed the satellite television DTH industry to change from being a largely hobbyist one where receivers were built in low numbers and complete systems were expensive (costing thousands of Dollars) to a far more commercial one of mass production.

Direct broadcast satellite dishes are fitted with an LNBF, which integrates the feedhorn with the LNB.

The satellite receiver demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.). Sometimes, the receiver includes the capability to unscramble or decrypt; the receiver is then called an Integrated receiver/decoder or IRD. The cable connecting the receiver to the LNBF or LNB must be of the low loss type RG-6, quad shield RG-6 or RG-11, etc. It cannot be standard RG-59.

[edit] Standards
Analog television distributed via satellite is usually sent scrambled or unscrambled in NTSC, PAL, or SECAM television broadcast standards. The analog signal is frequency modulated and is converted from an FM signal to what is referred to as baseband. This baseband comprises the video signal and the audio subcarrier(s). The audio subcarrier is further demodulated to provide a raw audio signal.

If the signal is a digitized television signal or multiplex of signals, it is typically QPSK.

In general, digital television, including that transmitted via satellites, are generally based on open standards such as MPEG and DVB-S.

The conditional access encryption/scrambling methods include BISS, Conax, Digicipher, Irdeto, Nagravision, PowerVu, Viaccess, Videocipher, and VideoGuard. Many conditional access systems have been compromised.

[edit] Categories of usage
There are three primary types of satellite television usage: reception direct by the viewer, reception by local television affiliates, or reception by headends for distribution across terrestrial cable systems.

Direct to the viewer reception includes direct broadcast satellite or DBS and television receive-only or TVRO, both used for homes and businesses including hotels, etc.

Friday, October 2, 2009
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Results 1-24 of 24 companies

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DIRECTV Inc
El Segundo, California

The DIRECTV Group, Inc. is a provider of digital television entertainment in the United States and Latin America. The business segments, DIRECTV U.S. and DIRECTV Latin America are engaged in acquiring, promoting, selling and/or distributing digital entertainment programming through... more
*
DISH Network Corporation
Englewood, Colorado

DISH Network Corporation is a provider of satellite delivered digital television to customers across the United States. DISH Network services include hundreds of video, audio and data channels, interactive television channels, digital video recording, high definition television,... more
*
EchoStar Communications Corporation
Inglewood, Colorado

EchoStar Corporation (EchoStar), formerly EchoStar Holding Corporation, will operate two primary businesses: digital set-top box business and a fixed satellite services business. EchoStar had a spin-off from DISH Network on January 1, 2008. The Company’s set-top box business designs,... more
*
Intelsat , Ltd.
Washington , Dc, District of Columbia

Intelsat Corporation is a provider of fixed satellite services worldwide and a provider of these services to each of the media and network services sectors. The Company provides service on a global fleet of 26 satellites that are integrated with 27 other satellites owned by other... more
*
GlobeCast
London, United Kingdom

GlobeCast, a subsidiary of France Telecom, is the leading global provider of content management and worldwide transmission services for professional broadcast delivery. The company operates a secure global satellite and fibre network to manage and transport 10 million hours of video... more
*
Telesat
Gloucester, Ontario, Canada

Telesat is a pioneer and world leader in satellite operations and systems management. The company made history in 1972 with the launch of the first Canadian commercial communications satellite in geostationary orbit. Today, Telesat competes with other top international satellite fleets in... more
*
Arqiva Limited
Winchester, Hampshire, United Kingdom

Arqiva has a 50-year history in transmission and has helped pioneer the technologies of the digital age. 22 million UK homes receive ITV, Channel 4 and Five via Arqiva's national transmitter networks. The company also provides transmission for most UK independent radio stations, both... more
*
Bell ExpressVu LP
North York, Ontario, Canada

Launched in September 1997, Bell ExpressVu is the largest and fastest growing direct-to-home (DTH) television company in Canada and the fifth largest broadcast distributor in the country with over 725,000 subscribers as of December 2000. Currently, the company offers more than 200 video... more
*
SES ASTRA
Austin, Texas

SES ASTRA operates the ASTRA Satellite System, offering a comprehensive portfolio of broadcast and broadband solutions for customers in Europe and beyond. ASTRA broadcasts television and radio programmes directly to millions of homes, and provides internet access and network services to... more
*
SES GLOBAL company

SES GLOBAL (Euronext Paris, Luxembourg Stock Exchange: SESG) wholly owns three market-leading satellite operators, SES ASTRA in Europe, SES AMERICOM in North America, and SES NEW SKIES, which provide global coverage and connectivity. The Company also holds strategic participations in... more
*
Sentech
Carrollton, Texas

Sentech has been at the leading edge of communication technology, pioneering the provisioning of broadcast signal distribution services. Sentech, a commercially operated, state-owned enterprise, is the largest signal distributor for broadcasting in Africa, transmitting programs for... more
*
Shaw Communications Inc
Calgary, Alberta, Canada

Shaw Communications Inc. is a communications company whose core business is providing broadband cable television, Internet, Digital Phone, telecommunications services (through Shaw Business Solutions) and satellite direct-to-home services (through Star Choice) to approximately 3.3 million... more
*
Arabsat

Backed by the 21 member countries of the Arab League, and with its 30-year heritage of continuous operations, Arabsat offers the Arab world an unrivalled range of satellite-based communications services such as Direct-to-Home Television and Radio, telephony, Internet and direct Broadband... more
*
MEASAT

*
Tata Sky Ltd.

Tata Sky Ltd., a joint venture of TATA and STAR, is committed to build a state-of-the-art Digital infrastructure for Pay Television in India. Tata Sky plans to introduce a nationwide Direct-to-Home (DTH) service that would allow it to reach every Indian home, however remote it may be. The... more
*
AlphaStar International Inc
Greenwich, Connecticut

AlphaStar is a 21st Century globally integrated Communications Company offering continuous full-motion high definition video, in IP multicasting and streaming formats, television and other multimedia programming services to the Internet through its uniquely positioned, high-bandwidth... more
*
Astro

Astro is Malaysia's leading multimedia broadcaster and producer of Malay, Chinese, Indian and English language programming content. It owns and operates the only direct-to-home satellite TV service with access to some 10 million viewers in over 2 million homes, representing 38% of TV... more
*
Pittsburgh International Telecommunications Inc
Pittsburgh, Pennsylvania

Pittsburgh International Telecommunications was established in 1983 as Mobile Satellite Communications, Inc. in Pittsburgh, Pennsylvania. The company provided mobile satellite uplinking services and owned and operated one C-Band transportable vehicle, which serviced the major television... more
*
ProtoStar LTD
San Francisco, California

ProtoStar is an Asian satellite services operator that was formed to acquire, launch and operate high-power geostationary satellites to lease capacity to Asian DTH and broadband service providers. The technical characteristics of its satellites and the configuration of the satellite... more
*
ASC Enterprises Limited
Lexington, Kentucky

*
Super Value Channel Inc
Pomona, California

SVC sells a variety of consumer products through DTH satellite TV, Cable TV, and over the internet. With full-scale TV production facility and multi-lingual "TV Shopping Experts" who may speak the ethnic languages to better service the customers, SVC is capable to broadcasting informative... more
*
SET Discovery Ltd.

SET Discovery Private Limited is a joint venture between SET India Pvt. Ltd. and Discovery Communications India. The company was set up in April 2002. Today, the company distributes 15 leading channels under the brand name of TheOneAlliance to over 61 million homes spread over 4000 cities... more
*
Atlanta DTH , Inc.
City Of Industry, California

Established in 1993, Atlanta DTH, Inc. is a leading supplier in the DTH satellite industry. We provide a complete product line of DTH satellite equipment such as IRD and LNBF, as well as customer-driven satellite network services and customer management system. ADTH's RV division... more
*
Cyfrowy Polsat S.A.

Launched in 1999, Cyfrowy Polsat offers today 35 television channels in the Polish language and five radio channels as well as hundreds of international Free-To-Air channels. The platform also offers interactive applications, such as TV banking, weather forecasts, SMS Chat, e-mail and... more
Posted by ramkumar at 9:26 AM 0 comments
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Sort By: Relevance (Default) Company Name Ascending Company Name Descending Revenue Results 1-24 of 24 companies


DIRECTV Inc
El Segundo, California

The DIRECTV Group, Inc. is a provider of digital television entertainment in the United States and Latin America. The business segments, DIRECTV U.S. and DIRECTV Latin America are engaged in acquiring, promoting, selling and/or distributing digital entertainment programming through... more


DISH Network Corporation
Englewood, Colorado

DISH Network Corporation is a provider of satellite delivered digital television to customers across the United States. DISH Network services include hundreds of video, audio and data channels, interactive television channels, digital video recording, high definition television,... more


EchoStar Communications Corporation
Inglewood, Colorado

EchoStar Corporation (EchoStar), formerly EchoStar Holding Corporation, will operate two primary businesses: digital set-top box business and a fixed satellite services business. EchoStar had a spin-off from DISH Network on January 1, 2008. The Company’s set-top box business designs,... more


Intelsat , Ltd.
Washington , Dc, District of Columbia

Intelsat Corporation is a provider of fixed satellite services worldwide and a provider of these services to each of the media and network services sectors. The Company provides service on a global fleet of 26 satellites that are integrated with 27 other satellites owned by other... more


GlobeCast
London, United Kingdom

GlobeCast, a subsidiary of France Telecom, is the leading global provider of content management and worldwide transmission services for professional broadcast delivery. The company operates a secure global satellite and fibre network to manage and transport 10 million hours of video... more


Telesat
Gloucester, Ontario, Canada

Telesat is a pioneer and world leader in satellite operations and systems management. The company made history in 1972 with the launch of the first Canadian commercial communications satellite in geostationary orbit. Today, Telesat competes with other top international satellite fleets in... more


Arqiva Limited
Winchester, Hampshire, United Kingdom

Arqiva has a 50-year history in transmission and has helped pioneer the technologies of the digital age. 22 million UK homes receive ITV, Channel 4 and Five via Arqiva's national transmitter networks. The company also provides transmission for most UK independent radio stations, both... more


Bell ExpressVu LP
North York, Ontario, Canada

Launched in September 1997, Bell ExpressVu is the largest and fastest growing direct-to-home (DTH) television company in Canada and the fifth largest broadcast distributor in the country with over 725,000 subscribers as of December 2000. Currently, the company offers more than 200 video... more


SES ASTRA
Austin, Texas

SES ASTRA operates the ASTRA Satellite System, offering a comprehensive portfolio of broadcast and broadband solutions for customers in Europe and beyond. ASTRA broadcasts television and radio programmes directly to millions of homes, and provides internet access and network services to... more


SES GLOBAL company

SES GLOBAL (Euronext Paris, Luxembourg Stock Exchange: SESG) wholly owns three market-leading satellite operators, SES ASTRA in Europe, SES AMERICOM in North America, and SES NEW SKIES, which provide global coverage and connectivity. The Company also holds strategic participations in... more


Sentech
Carrollton, Texas

Sentech has been at the leading edge of communication technology, pioneering the provisioning of broadcast signal distribution services. Sentech, a commercially operated, state-owned enterprise, is the largest signal distributor for broadcasting in Africa, transmitting programs for... more


Shaw Communications Inc
Calgary, Alberta, Canada

Shaw Communications Inc. is a communications company whose core business is providing broadband cable television, Internet, Digital Phone, telecommunications services (through Shaw Business Solutions) and satellite direct-to-home services (through Star Choice) to approximately 3.3 million... more


Arabsat

Backed by the 21 member countries of the Arab League, and with its 30-year heritage of continuous operations, Arabsat offers the Arab world an unrivalled range of satellite-based communications services such as Direct-to-Home Television and Radio, telephony, Internet and direct Broadband... more


MEASAT


Tata Sky Ltd.

Tata Sky Ltd., a joint venture of TATA and STAR, is committed to build a state-of-the-art Digital infrastructure for Pay Television in India. Tata Sky plans to introduce a nationwide Direct-to-Home (DTH) service that would allow it to reach every Indian home, however remote it may be. The... more


AlphaStar International Inc
Greenwich, Connecticut

AlphaStar is a 21st Century globally integrated Communications Company offering continuous full-motion high definition video, in IP multicasting and streaming formats, television and other multimedia programming services to the Internet through its uniquely positioned, high-bandwidth... more


Astro

Astro is Malaysia's leading multimedia broadcaster and producer of Malay, Chinese, Indian and English language programming content. It owns and operates the only direct-to-home satellite TV service with access to some 10 million viewers in over 2 million homes, representing 38% of TV... more


Pittsburgh International Telecommunications Inc
Pittsburgh, Pennsylvania

Pittsburgh International Telecommunications was established in 1983 as Mobile Satellite Communications, Inc. in Pittsburgh, Pennsylvania. The company provided mobile satellite uplinking services and owned and operated one C-Band transportable vehicle, which serviced the major television... more


ProtoStar LTD
San Francisco, California

ProtoStar is an Asian satellite services operator that was formed to acquire, launch and operate high-power geostationary satellites to lease capacity to Asian DTH and broadband service providers. The technical characteristics of its satellites and the configuration of the satellite... more


ASC Enterprises Limited
Lexington, Kentucky


Super Value Channel Inc
Pomona, California

SVC sells a variety of consumer products through DTH satellite TV, Cable TV, and over the internet. With full-scale TV production facility and multi-lingual "TV Shopping Experts" who may speak the ethnic languages to better service the customers, SVC is capable to broadcasting informative... more


SET Discovery Ltd.

SET Discovery Private Limited is a joint venture between SET India Pvt. Ltd. and Discovery Communications India. The company was set up in April 2002. Today, the company distributes 15 leading channels under the brand name of TheOneAlliance to over 61 million homes spread over 4000 cities... more


Atlanta DTH , Inc.
City Of Industry, California

Established in 1993, Atlanta DTH, Inc. is a leading supplier in the DTH satellite industry. We provide a complete product line of DTH satellite equipment such as IRD and LNBF, as well as customer-driven satellite network services and customer management system. ADTH's RV division... more


Cyfrowy Polsat S.A.

Launched in 1999, Cyfrowy Polsat offers today 35 television channels in the Polish language and five radio channels as well as hundreds of international Free-To-Air channels. The platform also offers interactive applications, such as TV banking, weather forecasts, SMS Chat, e-mail and... more

Posted by ramkumar at 9:26 AM 0 comments
This article contains weasel words, vague phrasing that often accompanies biased or unverifiable information. Such statements should be clarified or removed. (March 2009)

Satellite television is television delivered by the means of communications satellite and received by a satellite dish and set-top box. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.

Contents
[hide]
1 History
2 Technology
3 Standards
4 Categories of usage
4.1 Direct broadcast via satellite
4.2 Television receive-only
4.2.1 Direct to home television
4.2.2 Programming
4.2.3 Broadcasting centers
4.2.4 Encryption and transmission
4.2.5 The dish
4.2.6 The receiver
5 Satellite television by region and country
5.1 United States
5.2 India
5.3 Canada
5.4 United Kingdom
6 See also
7 References
8 External links


[edit] History
The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom 2 was launched in 1963. The world's first commercial communication satellite, called Intelsat I (nicknamed Early Bird), was launched into synchronous orbit on April 6, 1965. The first national network of satellite television, called Orbita, was created in Soviet Union in 1967, and was based on the principle of using the highly elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. The first domestic North American satellite to carry television was Canada’s geostationary Anik 1, which was launched in 1972.[1] ATS-6, the world's first experimental educational and Direct Broadcast Satellite, was launched in 1974. The first Soviet geostationary satellite to carry Direct-To-Home television, called Ekran, was launched in 1976.

[edit] Technology
Satellites used for television signals are generally in either naturally highly elliptical (with inclination of +/-63.4 degrees and orbital period of about 12 hours, also known as Molniya orbit) or geostationary orbit 37,000 km (22,300 miles) above the earth’s equator.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very large, as much as 9 to 12 meters (30 to 40 feet) in diameter. The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder 'retransmits' the signals back to Earth but at a different frequency band (a process known as translation, used to avoid interference with the uplink signal), typically in the C-band (4–8 GHz) or Ku-band (12–18 GHz) or both. The leg of the signal path from the satellite to the receiving Earth station is called the downlink.

A typical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Typical transponders each have a bandwidth between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees from the next satellite (to avoid interference). For Ku the spacing can be 1 degree. This means that there is an upper limit of 360/2 = 180 geostationary C-band satellites and 360/1 = 360 geostationary Ku-band satellites. C-band transmission is susceptible to terrestrial interference while Ku-band transmission is affected by rain (as water is an excellent absorber of microwaves at this particular frequency).

The downlinked satellite signal, quite weak after traveling the great distance (see inverse-square law), is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the flared front-end of a section of waveguide that gathers the signals at or near the focal point and 'conducts' them to a probe or pickup connected to a low-noise block downconverter or LNB. The LNB amplifies the relatively weak signals, filters the block of frequencies in which the satellite TV signals are transmitted, and converts the block of frequencies to a lower frequency range in the L-band range. The evolution of LNBs was one of necessity and invention.

The original C-Band satellite TV systems used a Low Noise Amplifier connected to the feedhorn at the focal point of the dish. The amplified signal was then fed via very expensive and sometimes 50 ohm impedance gas filled hardline coaxial cable to an indoor receiver or, in other designs, fed to a downconverter (a mixer and a voltage tuned oscillator with some filter circuitry) for downconversion to an intermediate frequency. The channel selection was controlled, typically by a voltage tuned oscillator with the tuning voltage being fed via a separate cable to the headend. But this design evolved.

Designs for microstrip based converters for Amateur Radio frequencies were adapted for the 4 GHz C-Band. Central to these designs was concept of block downconversion of a range of frequencies to a lower, and technologically more easily handled block of frequencies (intermediate frequency).

The advantages of using an LNB are that cheaper cable could be used to connect the indoor receiver with the satellite TV dish and LNB, and that the technology for handling the signal at L-Band and UHF was far cheaper than that for handling the signal at C-Band frequencies. The shift to cheaper technology from the 50 Ohm impedance cable and N-Connectors of the early C-Band systems to the cheaper 75 Ohm technology and F-Connectors allowed the early satellite TV receivers to use, what were in reality, modified UHF TV tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on 70 MHz where it was demodulated. This shift allowed the satellite television DTH industry to change from being a largely hobbyist one where receivers were built in low numbers and complete systems were expensive (costing thousands of Dollars) to a far more commercial one of mass production.

Direct broadcast satellite dishes are fitted with an LNBF, which integrates the feedhorn with the LNB.

The satellite receiver demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.). Sometimes, the receiver includes the capability to unscramble or decrypt; the receiver is then called an Integrated receiver/decoder or IRD. The cable connecting the receiver to the LNBF or LNB must be of the low loss type RG-6, quad shield RG-6 or RG-11, etc. It cannot be standard RG-59.

[edit] Standards
Analog television distributed via satellite is usually sent scrambled or unscrambled in NTSC, PAL, or SECAM television broadcast standards. The analog signal is frequency modulated and is converted from an FM signal to what is referred to as baseband. This baseband comprises the video signal and the audio subcarrier(s). The audio subcarrier is further demodulated to provide a raw audio signal.

If the signal is a digitized television signal or multiplex of signals, it is typically QPSK.

In general, digital television, including that transmitted via satellites, are generally based on open standards such as MPEG and DVB-S.

The conditional access encryption/scrambling methods include BISS, Conax, Digicipher, Irdeto, Nagravision, PowerVu, Viaccess, Videocipher, and VideoGuard. Many conditional access systems have been compromised.

[edit] Categories of usage
There are three primary types of satellite television usage: reception direct by the viewer, reception by local television affiliates, or reception by headends for distribution across terrestrial cable systems.

Direct to the viewer reception includes direct broadcast satellite or DBS and television receive-only or TVRO, both used for homes and businesses including hotels, etc.

[edit] Direct broadcast via satellite
Direct broadcast satellite, (DBS) also known as "Direct-To-Home" is a relatively recent development in the world of television distribution. “Direct broadcast satellite” can either refer to the communications satellites themselves that deliver DBS service or the actual television service. DBS systems are commonly referred to as "mini-dish" systems. DBS uses the upper portion of the Ku band, as well as portions of the Ka band.

Modified DBS systems can also run on C-band satellites and have been used by some networks in the past to get around legislation by some countries against reception of Ku-band transmissions.

Most of the DBS systems use the DVB-S standard for transmission. With Pay-TV services, the datastream is encrypted and requires proprietary reception equipment. While the underlying reception technology is similar, the Pay-TV technology is proprietary, often consisting of a Conditional Access Module and smart card.

This measure assures satellite television providers that only authorised, paying subscribers have access to Pay TV content but at the same time can allow free-to-air (FTA) channels to be viewed even by the people with standard equipment (DBS receivers without the Conditional Access Modules) available in the market.

[edit] Television receive-only
The term Television receive-only, or TVRO, arose during the early days of satellite television reception to differentiate it from commercial satellite television uplink and downlink operations (transmit and receive). This was before there was a DTH satellite television broadcast industry. Satellite television channels at that time were intended to be used by cable television networks rather than received by home viewers. Satellite TV receiver systems were largely constructed by hobbyists and engineers. These TVRO system operated mainly on the C band frequencies and the dishes required were large; typically over 3 meters (10 ft) in diameter. Consequently TVRO is often referred to as "big dish" or "Big Ugly Dish" (BUD) satellite television.

TVRO systems are designed to receive analog and digital satellite feeds of both television or audio from both C-band and Ku-band transponders on FSS-type satellites. The higher frequency Ku-band systems tend to be Direct To Home systems and can use a smaller dish antenna because of the higher power transmissions and greater antenna gain.

TVRO systems tend to use larger rather than smaller satellite dish antennas, since it is more likely that the owner of a TVRO system would have a C-band-only setup rather than a Ku band-only setup. Additional receiver boxes allow for different types of digital satellite signal reception, such as DVB/MPEG-2 and 4DTV.

The narrow beam width of a normal parabolic satellite antenna means it can only receive signals from a single satellite at a time. Simulsat or the Vertex-RSI TORUS, is a quasi-parabolic satellite earthstation antenna that is capable of receiving satellite transmissions from 35 or more C- and Ku-band satellites simultaneously.

[edit] Direct to home television
Today, most satellite TV customers in developed television markets get their programming through a direct broadcast satellite (DBS) provider, such as DISH TV or DTH platform. The provider selects programs and broadcasts them to subscribers as a set package. Basically, the provider’s goal is to bring dozens or even hundreds of channels to the customers television in a form that approximates the competition from Cable TV. Unlike earlier programming, the provider’s broadcast is completely digital, which means it has high picture and stereo sound quality. Early satellite television was broadcast in C-band - radio in the 3.4-gigahertz (GHz) to 7 GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (10 GHz to 14 GHz ). There are five major components involved in a direct to home (DTH) satellite system: the programming source, the broadcast center, the satellite, the satellite dish and the receiver.

Programming sources are simply the channels that provide programming for broadcast. The provider (the DTH platform) doesn’t create original programming itself; it pays other companies (HBO, for example, or ESPN or STAR TV or Sahara etc.) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between the viewer and the actual programming sources. (Cable television networks also work on the same principle.) The broadcast center is the central hub of the system. At the broadcast center or the Playout & Uplink location, the television provider receives signals from various programming sources, compresses these signals using digital compression (scrambling if necessary), and beams a broadcast signal to the proper satellite. The satellite receive the signal from the broadcast station and rebroadcast them to the ground. The viewer’s dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer’s house. The receiver processes the signal and passes it on to a standard television. These are the steps in greater detail:

[edit] Programming
Satellite TV providers get programming from two major sources: International turnaround channels (such as HBO, ESPN and CNN, STAR TV, SET, B4U etc) and various local channels (SaBe TV, Sahara TV, Doordarshan, etc). Most of the turnaround channels also provide programming for cable television, so sometimes some of the DTH platforms will add in some special channels exclusive to itself to attract more subscriptions. Turnaround channels usually have a distribution center that beams their programming to a geostationary satellite. The broadcast center uses large satellite dishes to pick up these analog and digital signals from several sources.

[edit] Broadcasting centers
The broadcast center converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of data — about 270 megabits per second (Mbit/s) for each channel. In order to transmit the signal from there, the broadcast center has to compress it. Otherwise, it would be too big for the satellite to handle. The providers use the MPEG-2 compressed video format — the same format used to store movies on DVDs. With MPEG-2 compression, the provider can reduce the 270-Mbit/s stream to about 3 or 10 Mbit/s (depending on the type of programming). This is the crucial step that has made DTH service a success. With digital compression, a typical satellite can transmit about 200 channels. Without digital compression, it can transmit about 30 channels. At the broadcast center, the high-quality digital stream of video goes through an MPEG-2 encoder, which converts the programming to MPEG-2 video of the correct size and format for the satellite receiver in your house.

[edit] Encryption and transmission
After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable data) if the receiver has the correct decoding satellite receiver with decryption algorithm and security keys. Once the signal is compressed and encrypted, the broadcast center beams it directly to one of its satellites. The satellite picks up the signal, amplifies it and beams it back to Earth, where viewers can pick it up.

[edit] The dish
A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam. The dish on the receiving end can’t transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point. The curved dish focuses incoming radio waves onto the feed horn. In this case, the point is the dish’s feed horn, which passes the signal onto the receiving equipment. In an ideal setup, there aren’t any major obstacles between the satellite and the dish, so the dish receives a clear signal. In some systems, the dish needs to pick up signals from two or more satellites at the same time. The satellites may be close enough together that a regular dish with a single horn can pick up signals from both. This compromises quality somewhat, because the dish isn’t aimed directly at one or more of the satellites. A new dish design uses two or more horns to pick up different satellite signals. As the beams from different satellites hit the curved dish, they reflect at different angles so that one beam hits one of the horns and another beam hits a different horn. The central element in the feed horn is the low noise blockdown converter, or LNB. The LNB amplifies the signal bouncing off the dish and filters out the noise (signals not carrying programming). The LNB passes the amplified, filtered signal to the satellite receiver inside the viewer’s house.

[edit] The receiver
Further information: Set-top box
The end component in the entire satellite TV system is the receiver. The receiver has four essential jobs: It de-scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that programming package. The provider can communicate with the chip, via the satellite signal, to make necessary adjustments to its decoding programs. The provider may occasionally send signals that disrupt illegal de-scramblers, as an electronic counter measure (ECM) against illegal users. It takes the digital MPEG-2 signal and converts it into an analog format that a standard television can recognize. Since the receiver spits out only one channel at a time, you can’t tape one program and watch another. You also can’t watch two different programs on two TVs hooked up to the same receiver. In order to do these things, which are standard on conventional cable, you need to buy an additional receiver. Some receivers have a number of other features as well. They pick up a programming schedule signal from the provider and present this information in an onscreen programming guide. Many receivers have parental lock-out options, and some have built-in Digital Video Recorders (DVRs), which let you pause live television or record it on a hard drive. While digital broadcast satellite service is still lacking some of the basic features of conventional cable (the ability to easily split signals between different TVs and VCRs, for example), its high-quality picture, varied programming selection and extended service areas are features now seen as an alternative. With the rise of digital cable, which also has improved picture quality and extended channel selection, the TV war is really heating up. Just about anything could happen in the next 10 years as all of these television providers battle it out.

[edit] Satellite television by region and country
This article contains weasel words, vague phrasing that often accompanies biased or unverifiable information. Such statements should be clarified or removed. (March 2009)

[edit] United States
It has been suggested that this section be split into a new article entitled Satellite television in the United States. (Discuss)

Currently, there are two primary satellite television providers of subscription based service available to United States consumers: Dish Network and DirecTV.

Over the past three decades, various U.S. satellite services have come and gone or combined to form the current primary services. In 1975 RCA created Satcom 1, the first satellite built especially for use by the then three national television networks (CBS, NBC, and ABC). Later that same year, HBO leased a transponder on Satcom 1 and began transmission of television programs via satellite to cable systems. Owners of cable systems paid $10,000 to install 3-meter dishes to receive TV signal in C-band. In 1976 Taylor Howard built an amateur system, which consisted of a converted military surplus radar dish and a satellite receiver designed and built by Howard, for home satellite reception. Taylor's system could be used for receiving TV programs both from American and Soviet communication satellites. In 1977 Pat Robertson launched the first satellite-delivered basic cable service called the CBN Cable Network. In 1979, the Satellite Home Viewers Act allowed homeowners in the US to own and operate their own home satellite system, consisting of C-band equipment from a multitude of manufacturers who were making parts for systems such as Taylor Howard's, and began a large controversy of which channels could be received by whom.

USSB was a direct-to-home service founded in 1981. In the early 1990s they partnered with Hughes and continued operation until purchased in 1998 by DirecTV.

In 1991 Primestar launched as the first North American DBS service. Hughes’s DirecTV, the first national high-powered upper Ku-band DBS system, went online in 1994. The DirecTV system became the new delivery vehicle for USSB. News Corporation currently holds a 38% stake, which it is in the process of selling to Liberty Media. In 1996, EchoStar’s Dish Network went online in the United States and has gone on to similar success as DirecTV’s primary competitor. The AlphaStar service launched in 1996 and went into bankruptcy in 1997. Dominion Video Satellite Inc's Sky Angel also went online in the United States in 1996 with its DBS service geared towards "faith and family". Primestar sold its assets to Hughes in 1999 and switched from DBS to an IPTV platform.

In 2004, Cablevision’s Voom service went online, specifically catering to the emerging market of HDTV owners and aficionados, but folded in April 2005. The service’s “exclusive” high-definition channels were migrated to the Dish Network system. Commercial DBS services are the primary competition to cable television service, although the two types of service have significantly different regulatory requirements (for example, cable television has public access requirements, and the two types of distribution have different regulations regarding carriage of local stations).



90cm multiple-LNA toroidal satellite dish
The majority of ethnic-language broadcasts in North America are carried on Ku band free-to-air. The largest concentration of ethnic programming is on Galaxy 25 at 97° W. Pittsburgh International Telecommunications and GlobeCast World TV offers a mix of free and pay-TV ethnic channels in the internationally-standard DVB-S format, as do others. Home2US Communications Inc. also offers several ethnic channels on AMC-4 at 101° W, as well as other free and pay-TV channels. Several U.S.-English language network affiliates (representing CBS, NBC, ABC, PBS, FOX, the CW (formerly the WB and UPN), ION Network and MyNetworkTV) are available as free-to-air broadcasts, as are the three U.S.-Spanish language networks (Univisión, Telefutura and Telemundo). The number of free-to-air specialty channels is otherwise rather limited. Specific FTA offerings tend to appear and disappear rather often and typically with little or no notice, although sites such as LyngSat do track the changing availability of both free and pay channels worldwide.[2]

[edit] India
The Indian Subcontinent have many service providers. They are Big TV(ADAG Group), Dish TV, Tata Sky(Tata and Sky), Sun DTH(Sun Group), DD Direct Plus(Prasar Bharathi), Airtel DTH(Bharathi) are some of them. Big TV, Sun DTH, Airtel DTH uses MPEG-4 technology for transmission the other providers use older technologies. DD Direct Plus offers free services while all other providers are subscription based.

[edit] Canada
Currently, there are two primary satellite television providers of subscription based service available to Canadians consumers: Bell TV and Shaw Direct.

[edit] United Kingdom
The leading satellite television broadcaster in the UK is a subscription based service named Sky Digital, marketed by British Sky Broadcasting. Since May 2008, a subscription free alternative known as Freesat has been available as part of preparations to migrate the UK to exclusively digital TV broadcasting. The Freesat service is run jointly by the UK's two largest broadcasters, ITV and BBC and should not be confused with the similarly named freesat from sky, a subscription free version of the Sky platform.

[edit] See also
Satellite dish
Microwave antenna
Commercialization of space
FTA Receiver
Molniya orbit
[edit] References
^ Robertson, Lloyd (1972-11-09). "Anik A1 launching: bridging the gap". CBC English TV. http://archives.cbc.ca/500f.asp?id=1-75-92-594. Retrieved 2007-01-25.
^ LyngSat tracking
[edit] External links
Lyngemark Satellite Charts
Worldwide satellite locations and feed information, available in a wide variety of languages
Upcoming Satellites
SES Astra interactive fleet map
SES Astra channel guide
Satellite-TV/TVRO/ C-Band FAQ List
Linowsat PID-Lists and Videobitrate Charts
Satellite and Digital Broadcasting
Steve Birkill's History of C-Band and Early Satellite TV
Mark Long's Russian Statsionar Satellite Systems
Online Satellite Calculations
Online Satellite Finder Based on Google Maps
[show] v • d • eCable, satellite and other specialty television providers

Cable television Asianet Cable Vision · Adams Cable · Adelphia · Airtel Digital Tv · Armstrong Telephone Company · Atlantic Broadband · Austar · Bright House Networks · Buckeye CableSystem · Cablelink · CableOne · Cable TV Hong Kong · Cable TV Wakasa Obama (Japan) · Cablevision (U.S.) · Cablevision (Canada) · Canal Digital · Champion Broadband · Charter · Cogeco · Columbus Communications · Comcast · Com Hem · Cox · DartyBox · EastLink · EMBARQ · ER-Telecom (Russia) · Fastweb (Italy) · First Media · Foxtel · GCI · Global Destiny · Globosat · GUdTV (Guam) · Hathway · Hot · IndosatM2 · Insight · Kabel Deutschland · Knology · Kujtesa · MASTV · MC Cable · MCV Broadband · Mediacom · MetroCast Cablevision · Midcontinent Communications · Millennium Digital Media · Neighbourhood Cable · Net Brasil · Ono · Optus · Persona · Qwest Choice TV · RCS&RDS · RCN · Rogers · Satview Broadband Ltd · Service Electric · SkyCable · Shaw · Smallworld · StarHub TV · Suddenlink · TDC · Tele2 · Tele Columbus (Germany) · Telenet (Belgium) · TelkomVision · TelstraClear InHomeTV · Time Warner · TransACT · TrueVisions · Turksat Kablo · TV Cabo · TVTEL · UCS · UPC Ireland · UPC Netherlands · UPC Romania · Uralsvyazinform (Russia) · Vidéotron · Virgin Media · WOW! · WightCable · Ziggo ·

Satellite television AB Sat · Airtel Digital Tv · AlphaStar · Arab Digital Distribution · ART · Astro · Astro Nusantara · Austar · Bell TV · BIG TV · Boom TV · CanalDigitaal · Canal Digital · CanalSat · CanalSat Calédonie · CanalSat Caraïbes · CanalSat Horizon · CanalSat Reunion · CaspioNet · Cyfra+ · D-smart · DD Direct Plus · DialogTV · Digi TV · Digit-Alb · Digital+ · Digiturk · DirecTV · Dish Network · Dish TV · Dolce · Dream · DStv · Euro1080 · Focus Sat · Foxtel · freesat · Freesat from Sky · Freeview (NZ) · GlobeCast World TV · Globosat · Glorystar · HiTV · Home2US · Indovision · Kristal-Astro · Max TV · MBC (Middle East) · N (Poland) · NOVA Cyprus · NOVA Greece · NTV Plus · Sky Deutschland · Orbit Showtime · PrimeStar · SelecTV · Shaw Direct · Sky Digital · SKY Italia · Sky Latin America · SkyLife · Sky PerfecTV! · SKY TV (NZ) · STAR Select · STAR TV · Sun TV · Tata Sky · Tivù Sat · TPS · TelkomVision · TrueVisions · TV Cabo · TV Vlaanderen Digitaal · TVTEL · UBI World TV · USSB · Viasat · Viasat Ukraine · Voom · WOWOW · Yes

IPTV Aliant TV · Alice Home TV (Italy) · Beeline (Russia) · Belgacom · BSNL · BT Vision · Canal Digital · Clix · Crnogorski Telekom · DartyBox · Deutsche Telekom (T-Home) · Elioni DTV (Estonia) · Fastweb (Italy) · Fine TV · Free · Freewire TV · hanaTV (Korea) · Imagenio · iNES · Infostrada TV (Italy) · KPN · La Télé des P&T (Luxembourg) · Maroc Telecom TV (Morocco) · mio TV · MTNL · Neuf · now TV · Orange · Portugal Telecom (Meo) · Sky Angel · T-com Hrvatska · T-Home Macedonia · TELE2 · Telefónica · TeliaSonera · Telus TV · Tiscali TV (Italy) · Tiscali TV (UK) · TPG IPTV · TrueIPTV (Thailand) · TVCatchup · U-verse · VDC · Viasat

Terrestrial television Boxer (Sweden) · Cablevision (Lebanon) · Doordarshan · Freeview (Australia) · Freeview (NZ) · Freeview (UK) · KPN (The Netherlands) · La 7 Cartapiù (Italy) · Mediaset Premium (Italy) · MiTV · Multi-Choice TV (Barbados) · Pakistan Television Corporation · PlusTV (Finland) · RiksTV (Norway) · Sky Picnic · Télévision Numérique Terrestre (France) · Top Up TV · Televisão Digital Terrestre (Portugal)

Fiber-Optic TVTEL · Verizon FiOS · at&t · meo fibra

[show] v • d • eWireless video and data distribution methods

Advanced Wireless Services · Amateur television · Analog television · Digital radio · Digital television · Digital television in Europe · Digital terrestrial television (DTT or DTTV) ·
Digital Video Broadcasting: ( Terrestrial - Satellite - Handheld ) · DVB-MS · Ku band · Local Multipoint Distribution Service (LMDS) · Microwave · Mobile TV · Multichannel Multipoint Distribution Service (MMDS) now known as Business Radio Service (BRS) · Instructional Television Fixed Service (ITFS) now known as Educational Broadband Service (EBS) · MVDS · MVDDS · Satellite Internet access · Satellite radio · Satellite television · Wi-Fi · WiMAX · Wireless local loop



Retrieved from "http://en.wikipedia.org/wiki/Satellite_television"
Categories: Satellite television | Broadcasting | Satellite ground stations
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Posted by ramkumar at 9:23 AM 0 comments
http://pib.nic.in/focus/foyr2001/fomar2001/dth_glines.pdf
Posted by ramkumar at 9:18 AM 0 comments
TV Broadcast URI Schemes
Requirements
W3C Note 21 October 1999
This version:
http://www.w3.org/TR/1999/NOTE-TVWeb-URI-Requirements-19991021
Latest version:
http://www.w3.org/TR/TVWeb-URI-Requirements
Previous version:
http://www.w3.org/TR/1999/NOTE-TVWeb-URI-Requirements-19991019
Editors:
Warner ten Kate (warner.ten.kate@philips.com)
Gomar Thomas (gomer@lgerca.com)
Craig Finseth (craig@finseth.com)
Copyright © 1999 W3C (MIT, INRIA, Keio), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.


--------------------------------------------------------------------------------

Status of this document
This Note was produced by the W3C TV-Web Interest Group. It is the result of discussions on URI schemes suited for use in TV Broadcast environments. The document reflects preliminary results, and is intended to serve as a base to further work to design TV Broadcast URIs. Please send comments to the TV-Web mailing list www-tv@w3.org.

This version is an update of the version dated 19 October 1999, fixing a wrong link.

Publication of a W3C Note does not imply endorsement by the entire W3C Membership. A list of current W3C technical reports and publications, including Working Drafts and Notes, can be found at http://www.w3.org/TR.

This section represents the status of this document at the time this version was published. It will become outdated if and when a new version is published.

Table of Contents
Abstract
1. TV Broadcast: Definition and scope
2. Application Scenarios
3. Requirements on Global TV Broadcast URI schemes
4. Exceptions in TV Broadcast URIs
References
Abstract
This document is an informational document and discusses the requirements posed to URI schemes for identifying resources in Television (TV) Broadcast environments. The document is the outcome of discussions on this subject by the W3C TV-Web Interest Group [TVWebIG, TVWebMail].

Typical use cases are summarized where TV Broadcast URIs are involved. A distinction is made between Global and Local usage. Also, a hierarchy of resource types is identified. Requirements related to the Global usage case are listed.

1. TV Broadcast: Definition and scope
Definition of TV Broadcast
In this document TV Broadcast is used as the generic term to refer to currently existing TV systems, their transport protocols, and their typical operation of content provision and distribution. TV Broadcast concerns both digital and analog systems and includes systems like DVB, ATSC, DSS, NTSC, and PAL. The TV Broadcast "network layer" is typically non-IP based.

The term TV Broadcast URI refers to URIs which identify, and possibly locate, TV Broadcast content. In this document "URI" is used to indicate TV Broadcast URI.

Typically, TV Broadcast systems are push systems. The content streamed along a TV Broadcast transport is scheduled by the service provider; the user has no influence on that. In this model the user accesses the stream(s) rather than the server at the upstream station.

Hierarchy in TV Broadcast content
TV Broadcast content is modeled in a four-layer hierachy, consisting of service, event, component, and fragment. Service is at the top, fragment is at the bottom of the hierarchy.

The term service is used to refer to a concatenation of programs, all being broadcast by the same service provider. The programs of a service share some tuning characteristics. Service corresponds to the naming "channel" as used in today's analog TV.

The term event is used to refer to a single TV program. An event consumes a time period within a service and therefore can be characterized with begin and end times. The service provider determines the granularity in which the service is split in events. An event can be a complete program or an episode of a program. Events can be grouped in series, e.g., to form a serial. Events are the typical entities which EPGs list to present program schedule information.

The term component is used to refer the constituents of an event. The audio and video of a TV program are obvious examples. In case of multilingual programs there are multiple audio components. In case of interactive programs the components are the application documents and the other data these applications are using. Next to continuous data like audio and video, component also encompasses discrete data like Web pages and applications describing composition and interactivity. The URI identifying an application can constitute the base URI for the further components referenced by that application.

The term fragment is used to refer to a subpart of a component. For instance, it can be a slice of a video sequence, or a subregion in an image.

Due to the push character of TV Broadcast there are two dimensions of hierarchy, a schedule related and a content related. The first is the hierarchy of transport system, transport stream, service, series, event; The second is the hierarchy of series, event, component, fragment.

The term resource is to be understood as in RFC 2396, sec.1.1 [RFC2396]. In the context of TV Broadcast a resource refers to the entities service, event, component, and fragment in particular.

Setting and usage of TV Broadcast URIs
TV Broadcast applications need a mechanism to identify and locate the components building the application. The URI scheme is a useful tool for that as it opens possibilities for seamless transition in referencing resources at TV Broadcast transport and Internet sites. URI schemes to locate resources at the Internet are well-known, and are not further observed in this document. URI schemes to locate resources in a TV Broadcast transport channel have been proposed, but most are designed with a particular TV Broadcast transport environment in mind.

Next to locating components at TV Broadcast transport channels, another aspect of TV Broadcast URIs concerns referencing the events. In the first place, events are accessible at the TV Broadcast transport channel, possibly at several channels and at multiple periods of time. The above mentioned URI schemes also address this aspect, but all in their own way. In the second place, the content may be stored and made available through another path than the TV Broadcast transport channel. Most evident are local storage, like VCR-type of devices, and the Internet itself. Local storage devices can be connected through an in-home network to the user agent presenting the application. Local storage in the sense of the client's local file system or in the sense of cache buffering are not observed in this document.

TV Broadcast content delivered through a so-called IP-tunnel is considered as content made available through the Internet. An IP-tunnel refers to a forwarding path which is logically separated from the conventional TV Broadcast transport protocol but uses the same physical transmission link.

2. Application Scenarios
Application types, further definition and scope
Applications can be distinguished in usage of URIs for Global and Local scope.

Global refers to URIs contained in documents which can be accessed anywhere around the world, and which identify content related to any TV Broadcast system in the world, including storage devices associated with that TV Broadcast system. Such a global URI may include identification of the TV Broadcast system to be used.

Local refers to URIs contained in documents which are accessed within a certain TV Broadcast system, and which identify content to be accessed through that TV Broadcast system. URIs that reference content outside the local TV Broadcast system, are assumed to be either Global URIs or traditional URIs for locating resources at the Internet.

This document concentrates on Global URIs, as those have a world-wide interest for standardization. It would be nice when Local URIs bear an identical format, but that is considered not a necessary requirement. Local URIs can be specified within their respective application domains. On the other hand, it would be nice when Global URIs can serve as a base URI for Local URIs, either as direct copy or by some mapping function.

Further, URIs can be distinguished in identifying a service or event, and in identifying a particular content item (component or fragment) in such a service or event. This reflects the two dimensions observed above of schedule related and content related hierarchy. The use cases where a content item in a certain service is to be identified while the context isn't already that service, seem rare. Consequently, a URI is not required to carry both informations (service and content item) together.

This distinction suggests that identification of a particular content item belongs to the Local class of URIs, and that Global URIs typically identify a service or an event. However, an exception can be found in the case where the same content item is referenced in various transport contexts, e.g. in a commercial.

An important class of Global URIs identify their resource in a location and time independent way, i.e. independent of the particular TV Broadcast transport system and particular schedule. For instance, they are also valid after local storage. As such, they resemble URN behavior, opposed to URL behavior.

As the set of resources and their various locations can scale to large numbers, it is preferred that the URI scheme imposes a hierarchical structure, certainly when the URI's purpose is to locate a resource. A hierarchy allows for step-by-step resolution and navigation to the resource identified. By that, efficiency and scalability is improved. Further, implying a hierarchical structure allows to group resources, and by that to distinguish between, for example, in identifying a serial and an event in that serial.

Use cases, both Local and Global URI
Below, some representative use cases are listed. An exhaustive list of application scenarios is provided in [USECASES].
Basic EPG type of locating:
Reference TV Broadcast services and events from a Web page for navigating to them. The references are tolerant to modifications in the actual transmission schedule, but a coarse indication can be derived. The broadcast program can be indicated through tuning data or through naming. Next to navigation to the program, the EPG also supports for setting reminders or recording of programs. Instead of a single program, the serial of which the program is part, is referred to, such that setting a reminder or a recording for all episodes can be accomplished. It is the year 2002. Fox is broadcasting a World Cup game from South Korea in both analog and digital formats, with the broadcast reaching North America, Europe, Africa, Asia, Latin America, Australia, etc., through a wide variety of local affiliates and re-broadcast operators. Fox wishes to put a hyperlink to the broadcast on its web site, so that users of Internet-connected TV receivers all over the world with the right software (perhaps native, perhaps downloaded) can click on the hyperlink and have their receivers tune to the broadcast (or set a reminder for the broadcast, if the game is not currently on).
A sports fanatic wants to watch all the above broadcasts by Fox. Therefore he records all the broadcasts and copies the above Fox World Cup page to his local disc. From that page he can access the broadcasts or, when they have been recorded, view them from his recording device. At its site Fox also provides the transmitted broadcasts, albeit at high compression rates. The page will direct users who haven't recorded the broadcast to these videos.
A Web page is composed for presentation on a TV Broadcast receiver. The Web page is delivered in association with a TV Broadcast program (the transmission paths may be physically separated). The Web page includes an object which refers to the associated audio/video image of the TV broadcast program.
In a Web page a TV Broadcast event is referred, but the exact location is not known at authoring time. The URI is incomplete in its information. Instead a query is added to retrieve the missing information. When the available TV Broadcast system supports the query mechanism, the URI can be resolved and the identified resource can be retrieved. The query language is technology-independent, i.e. it is not relying on specific fields, such as SI data, in the TV Broadcast transmission system.
Examples are:
dtv://?program=X-Files dtv://ABC/?lang=sp A TV Broadcast of a soccer match is data-enhanced; in a data carousel module or an encapsulated IP datagram a file is contained which gives up-to-the-second statistics on goals scored, fouls committed, corner kicks taken, shots at goal, shots on goal, etc. The broadcaster wants to put a URI on their web site which references this file, allowing applications on Internet-connected TV receivers all over the world to get to the file and display it in nifty ways.
A data file is transmitted along with a TV program, the data file is containing additional information to that program. It also contains hyperlinks to the programs and/or data in other data files being broadcast on the same channel and in other channels, so that receivers can set reminders for the upcoming game and/or data file.
A Web page is transmitted with a TV Broadcast commercial. The commercial is about an upcoming TV Broadcast program. The viewer can click a hotspot area such as to set a reminder for that program. The Web page can also be accessed at the broadcaster's Web site.
A set of three Web page is transmitted with a TV Broadcast commercial. The viewer can navigate the three pages. The pages are transmitted frequently along various TV Broadcast systems. The pages can also be accessed at the advertiser's Web site, where they are maintained at a particular sub directory. Therefore, the advertiser uses relative referencing between the pages.
A live quiz show is enhanced such that the viewer can play along. The enhancement data are a mixture of Web pages, which compose the quiz's question and answer environment, element values, which carry the actual questions and (correct) answers to be inserted in the Web pages, and procedural cells to control the viewer's score. The Web pages are provided at a Web site long before the show is aired, such that viewers can prepare. The element values are transported along the TV Broadcast transmission channel during the show. They are synchronized with the actions in the show such as to complete and update the application.
There are several levels of play along: some pages provide the viewer with hints such as to ease answering, and some pages provide less alternatives in the multiple choice questions. The viewer can select his level by navigating between these pages.
Upon the actual broadcast an application is broadcast with the program to initiate the enhancement. The application references the Web site, such that upon tuning to the TV Broadcast the Web site's home page gets retrieved. Triggered by stream events in the TV Broadcast transport stream, the application also controls the insertion of element values (questions and answers) and the score management (e.g., no score increment after answer presentation).
A Web site provides a EPG covering programs transmitted world-wide. A viewer is visiting this site and browses the EPG. Upon encountering his favorite movie "Once upon a time in the Cyber" he clicks the item on the EPG. Regretfully, the movie isn't scheduled for the 419 TV Broadcast satellites his receiver is configured to. Instead of setting a reminder, the receiver informs the user the movie will not appear on his reception links.
3. Requirements on Global TV Broadcast URI schemes
Conventions used in this document
In this document three levels of priority are used to indicate the desirability of a requirement.

MUST
The key word "MUST" is to be understood as an essential and critical requirement.
SHOULD
The key word "SHOULD" indicates an important requirement.
MAY
The key word "MAY" indicates a useful feature.
[These key words and their meaning are based upon RFC 2119 [RFC2119]. That RFC specifies similar wording for implementation compliance with a protocol specification. In this document the wording reflects specification compliance with protocol goals.]

Requirements
The URI scheme MUST comply with RFC 2396 [RFC2396].
Where the URI serves as a name identifier (URN), the corresponding URN specifications MUST be taken into account, e.g. [RFC2141, RFC2168].
Where the URI serves as a locator identifier (URL), the definition of the URI scheme MUST follow the guidelines as set forth in [URLGUIDE].
The URI MAY support queries to be posed to the TV Broadcast receiver. The query language MUST be independent to the TV Broadcast system.
The URI scheme SHOULD support relative referencing such that a TV-program with all its associated resources can be referenced against a common base, which is the TV Broadcast URI of that aggregate.
Where the URI serves as a locator identifier (URL), the URI scheme SHOULD include a hierarchical structure either to identify the resoure as a service or an event from a service, or to identify the resource as an event, a component from an event, or a fragment from a component. The structure SHOULD provide optional levels to group events into series or serials and to group components into composites.
Where the URI serves as a name identifier (URN), the URI scheme MAY include such hierarchical structure.
The URI scheme SHOULD support the spectrum of transport protocols applied and standardized in TV Broadcast systems. This includes both audio/video and data broadcast protocols.
A URI MUST be invariant with respect to the normal range of transport stream transformations along the path from provider to user, both in referencing the time and the location of the resource in that transport stream.
Given a URI, it MUST be possible for a receiver to actually locate the resource, or conclude that it is not reachable.
A URI MUST be meaningful when interpreted, independent of the transmission context in which the URI is called. Transmission context refers to a coherent set of content streams as they arrive at the receiver. An example is a set of TV broadcast services sharing a same physical connection; another is an Internet connection. In case the context is the same transmission system as in which the content is located, the URI MUST be resolvable.
Where the URI serves as a name identifier (URN), it SHOULD be resolvable under any of the following network access conditions:
TV Broadcast
Internet
In Home/local storage
The actual resource's retrieved content data MAY differ in terms of content encoding, content quality, performance, and edit version.
Where the URI serves as a name identifier (URN), the scheme MUST support referencing various instantiations of the same content (encoding, quality/compression ratio, versions/edits).
Any actual scheme SHOULD be coordinated with standardisation bodies such as ATSC, DVB, and DAVIC, and SHOULD be reasonably acceptable to those bodies.
The URI scheme MUST interoperate with the Internet access schemes, such as to enable seamless transition in referencing resources at TV Broadcast or Internet sites.
4. Exceptions in TV Broadcast URIs
TV Broadcast differs from the conventional Internet in several ways. The TV Broadcast URI scheme is affected by that in the following aspects:
The host is not necessarily a server identifiable through an IP-address. For instance, the "host" is a transport stream.
The resource access and retrieval scheme is not necessarily IP-stack based.
The resource's availability implicitly depends on, or at least relates to, a transmission schedule.
Because TV Broadcast is a resource constrained environment, it is worthwhile to keep the length of the URI limited. This document does not pose a requirement on a maximum length of a TV Broadcast URI. It is left to the particular application domain to specify such limitations.

References
[RFC2119] Key words for use in RFCs to Indicate Requirement Levels,
RFC 2119, S. Bradner. March 1997.
[TVWebIG] W3C TVWeb Interest Group,
Group page of the W3C TV-Web IG. Philipp Hoschka.
[TVWebMail] TV-Web Mail Archives,
Threads starting with messages 0040, 0041, and 0046. Oct/Nov 1998.
.
[RFC2396] Uniform Resource Identifiers (URI): Generic Syntax,
RFC 2396, T. Berners-Lee, R. Fielding, L. Masinter. Aug. 1998.
[RFC2141] URN Syntax,
RFC 2141, R. Moats. May 1997.
[RFC2168] Resolution of Uniform Resource Identifiers using the Domain Name System,
RFC 2168, R. Daniel, M. Mealling. June 1997.
[URLGUIDE] Guidelines for new URL Schemes,
Internet-Draft, L. Masinter, H.T. Alvestrand, D. Zigmond, R. Petke. March 1999.
[USECASES] Applications list,
Posting to the TV-Web IG, C. Finseth. December 1998.
Posted by ramkumar at 9:13 AM 0 comments
http://www.broadcast-equipment.net
Posted by ramkumar at 9:12 AM 0 comments
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